Protective anode coatings for high energy batteries

ABSTRACT

Materials for coating a metal anode in a high energy battery, anodes coated with the materials, and batteries incorporating the coated anodes are provided. Also provided are batteries that utilize the materials as electrolytes. The coatings, which are composed of binary, ternary, and higher order metal and/or metalloid oxides, nitrides, fluorides, chlorides, bromides, sulfides, and carbides limit the reactions between the electrolyte and the metal anode in a battery, thereby improving the performance of the battery, relative to a battery that employs a bare anode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage of International ApplicationNo. PCT/US2017/021365 that was filed Mar. 8, 2017, the entire contentsof which are hereby incorporated by reference; which claims priority toU.S. provisional patent application No. 62/306,866 that was filed Mar.11, 2016, the entire contents of which are hereby incorporated byreference.

REFERENCE TO GOVERNMENT RIGHTS

This invention was made with government support under DE-AC02-06CH11357(Subcontract 9F-31901 from Argonne National Laboratories to NorthwesternUniversity) awarded by the Department of Energy and DMR1309957 awardedby the National Science Foundation. The government has certain rights inthe invention.

BACKGROUND

The energy density of batteries is a critical bottleneck limiting theperformance of portable electronics and electric vehicles. Lithiumbatteries offer superlative energy density, and for two decades,incremental improvements in materials, chemistry, and cell engineeringhave increased energy density from 250 to 650 Wh/L. While there are manyongoing efforts to increase energy density, most approaches offer onlyincremental improvements. For example, substituting a new Li₂MnO₃*LiMO₂cathode material for state-of-the-art LiNi_(0.8)Co_(0.15)Al_(0.05)O₂offers only 7% improvement in cathode energy density. (See, Croy, J. R.;Abouimrane, A.; Zhang, Z. Next-Generation Lithium-Ion Batteries: thePromise of Near-Term Advancements. MRS bulletin 2014, 39, 407-415.)Similarly, substituting a new silicon-carbon composite anode for aconventional graphite anode offers only 20% improvement in cell energydensity. (See, Obrovac, M. N.; Chevrier, V. L. Alloy Negative Electrodesfor Li-Ion Batteries. Chem. Rev. 2014, 114, 11444-11502.)

Metal anodes, which are comprised entirely or almost entirely of themobile element in a battery, present a rare opportunity for majorimprovement in energy density. For example, in a lithium battery with aLiNi_(0.8)Co_(0.15)Al_(0.05)O₂ cathode, energy density can be doubled bysubstituting a lithium metal anode in place of a conventional graphiteanode. (See, McCloskey, B. D. The Attainable Gravimetric and VolumetricEnergy Density of Li—S and Li-Ion Battery Cells with SolidSeparator-Protected Li-Metal Anodes. J. Phys. Chem. Lett. 2015, 6 (22),4581-4588.) This doubling in energy density is attainable because metalanodes can eliminate host materials, polymeric binders,electrolyte-filled pores, and even copper current collectors from theanode. (See, Hovington, P.; Lagacé, M.; Guerfi, A.; Bouchard, P.;Mauger, A.; Julien, C. M.; Armand, M.; Zaghib, K. New Lithium MetalPolymer Solid State Battery for an Ultrahigh Energy: Nano C—LiFePO₄Versus Nano Li_(1.2)V₃O₈ . Nano Lett. 2015, 15, 2671-2678.) Metal anodesalso offer the lowest possible anode redox potential and therefore thehighest possible cell voltage. In batteries where Na or Mg is the mobileelement, metal anodes eliminate the need for anode host materials, whichoften exhibit poor capacity, kinetics, and reversibility for theseelements. (See, Seh, Z. W.; Sun, J.; Sun, Y.; Cui, Y. A HighlyReversible Room-Temperature Sodium Metal Anode. ACS Cent. Sci. 2015, 1(8), 449-455; Saha, P.; Datta, M. K.; Velikokhatnyi, O. I.; Manivannan,A.; Alman, D.; Kumta, P. N. Rechargeable Magnesium Battery: CurrentStatus and Key Challenges for the Future. Progress in Materials Science2014, 66, 1-86.)

A major challenge for the implementation of metal anodes is reactivitybetween the metals and electrolytes. Metal anodes must beelectropositive to provide a sufficient cell voltage, but thiselectropositivity causes the metals to drive electrochemical reductionof electrolytes. Both liquid and solid electrolytes are often reactiveat the anode surface. For graphite anodes in conventional lithium-ionbatteries, reactivity can be mitigated by a passivation layer that formsin situ from the reaction products. This passivation layer must bemechanically durable, electronically insulating to block electrontransfer from the anode to the electrolyte, and chemically stable ormetastable. For metal anodes, there is sparse evidence for passivationby in situ reactivity. Reactivity at the surface of metal anodes causesimpedance growth that destroys cell performance, according to Luntz etal. (See, Luntz, A. C.; Voss, J.; Reuter, K. Interfacial Challenges inSolid-State Li Ion Batteries. J. Phys. Chem. Lett. 2015, 6, 4599-4604.)These authors argue that “the principal hurdle for developing successfulsolid-state batteries for EVs is in minimizing the interfacialimpedances between the [solid electrolyte] and the electrodes and not inmaximizing the conductivity in the [solid electrolytes].”

To limit reactivity between metal anodes and electrolytes, coatingmaterials can be deposited on the metal surface prior to cell assembly.These coatings typically range between one nanometer and one micrometerin thickness. Similar to passivation layers, these coatings should bedurable and electronically insulating to block transfer of electrons.Unlike passivation layers, these coatings can be deposited at elevatedtemperatures from a variety of precursors, allowing for greater controlof coating characteristics. Anode coatings function as an additionalelectrolyte layer and can be used in conjunction with other liquid orsolid electrolytes. Li metal anodes have been protected with a varietyof coatings including Li₃N, Li₃PO₄, and Al₂O₃. (See, Ma, G.; Wen, Z.;Wu, M.; Shen, C.; Wang, Q.; Jin, J.; Wu, X. Lithium Anode ProtectionGuided Highly-Stable Lithium-Sulfur Battery. Chem. Commun. 2014, 50,14209-14212; Kuwata, N.; Iwagami, N.; Tanji, Y.; Matsuda, Y.Characterization of Thin-Film Lithium Batteries with Stable Thin-FilmLi3PO4 Solid Electrolytes Fabricated by ArF Excimer Laser Deposition. J.Electrochem. Soc. 2010, 157 (4), A521-A527; Kozen, A. C.; Lin, C.-F.;Pearse, A. J.; Schroeder, M. A.; Han, X.; Hu, L.; Lee, S.-B.; Rubloff,G. W.; Noked, M. Next-Generation Lithium Metal Anode Engineering viaAtomic Layer Deposition. ACS nano 2015, 9 (6), 5884-5892; Kazyak, E.;Wood, K. N.; Dasgupta, N. P. Improved Cycle Life and Stability ofLithium Metal Anodes Through Ultrathin Atomic Layer Deposition SurfaceTreatments. Chem. Mater. 2015, 27, 6457-6462.) Anode coatings, likeelectrolytes, can also react with the anode metal. Thus, durablebatteries with metal anodes require selection of anode coatings that arestable in contact with the anode metal.

SUMMARY

One aspect of the invention provides coated lithium metal anodes forhigh energy batteries. Also provided are batteries incorporating thecoated lithium metal anodes.

One embodiment of a coated lithium metal anode includes: a lithium metalanode; and a coating on at least a portion of the lithium metal anode,wherein the coating comprises a metal sulfide selected from SrS, CaS,YbS, and combinations thereof. One embodiment of a lithium batteryincorporating the coated lithium metal anode includes: the coatedlithium metal anode; a cathode in electrical communication with thecoated lithium metal anode; and an electrolyte disposed between thecoated lithium metal anode and the cathode. The electrolyte can be, forexample, a sulfide solid electrolyte.

Another embodiment of a coated lithium metal anode includes: a lithiummetal anode; and a coating on at least a portion of the lithium metalanode, wherein the coating comprises a metal oxide selected from rareearth metal oxides, ternary lithium oxides other than Li₃PO₄, quaternarylithium oxides, calcium oxide, or a combination thereof, and furtherwherein the metal oxide is stable; exhibits chemical equilibrium withthe lithium metal anode; and is electrically insulating. One embodimentof a lithium battery incorporating these coated lithium metal anodesincludes: the coated lithium metal anode; a cathode in electricalcommunication with the coated lithium metal anode; and an electrolytedisposed between the coated lithium metal anode and the cathode. Thecoating can be composed of, for example, Li₂HfO₃ and/or Li₇La₃Hf₂O₁₂.The electrolyte can include, for example, a lithium salt in an organicsolvent, such as a carbonate, an ether, or an acetal, or can be a solidelectrolyte, such as a solid polymer electrolyte, an oxide solidelectrolyte, a phosphate solid electrolyte, or a nitride solidelectrolyte. Although, other electrolytes could be used. In onevariation of this embodiment, the coating is composed of Li₇La₃Hf₂O₁₂and the electrolyte is a Li₇La₃Zr₂O₁₂ oxide solid electrolyte. In somesuch variations, the anode coating material is a garnet-structuredgradient material having the composition Li₇La₃Zr₂O₁₂ at the solidelectrolyte interface and the composition Li₇La₃Hf₂O₁₂ at the lithiummetal anode surface. The metal oxide coating can also be composed of,for example, a rare earth metal oxide having the formula R₂O₃, where Ris selected from Dy, Er, Gd, Ho, La, Lu, Nd, Pr, Sm, Tm, and Y; or arare earth metal oxide having the formula LiRO₂, where R is selectedfrom Dy, Er, Gd, Ho, Sc, and Tb. The electrolyte can include, forexample, a lithium salt in an organic solvent, such as a carbonate, anether, or an acetal, or can be a solid electrolyte, such as a solidpolymer electrolyte, an oxide solid electrolyte, a phosphate solidelectrolyte, or a nitride solid electrolyte. Although other electrolytescould be used.

Another embodiment of a coated lithium metal anode includes: a lithiummetal anode; and a coating on at least a portion of the lithium metalanode, wherein the coating comprises a metal halide selected from metalfluorides other than LiF, metal chlorides, and metal bromides, and themetal of the metal halide comprises an alkali metal, an alkaline earthmetal, or a rare earth metal, and further wherein metal halide isstable; exhibits chemical equilibrium with the lithium metal anode; andis electrically insulating. One embodiment of a lithium batteryincorporating these coated lithium metal anodes includes: the coatedlithium metal anode; a cathode in electrical communication with thecoated lithium metal anode; and an electrolyte disposed between thecoated lithium metal anode and the cathode. The coating can be composedof, for example, a metal halide selected from CaF₂, SrF₂, YbF₂, EuF₂, ora combination thereof; YbCl₂; YbBr₂, BaBr₂, SrBr₂, EuBr₂, or acombination thereof; and/or LiCl, NaCl, KCl, RbCl, CsCl, or acombination thereof. The electrolyte can include, for example, a lithiumsalt in an organic solvent, such as a carbonate, an ether, or an acetal,or can be a solid electrolyte, such as a solid polymer electrolyte, anoxide solid electrolyte, a phosphate solid electrolyte, or a nitridesolid electrolyte. Although, other electrolytes could be used. In somevariations of these batteries, the electrolyte is a sulfide solidelectrolyte.

Another embodiment of a coated lithium metal anode includes: a lithiummetal anode; and a coating on at least a portion of the lithium metalanode, wherein the coating comprises a ternary lithium nitride, whereinthe ternary lithium nitride is stable; exhibits chemical equilibriumwith the lithium metal anode; and is electrically insulating. Oneembodiment of a lithium battery incorporating these coated lithium metalanodes includes: the coated lithium metal anode; a cathode in electricalcommunication with the coated lithium metal anode; and an electrolytedisposed between the coated lithium metal anode and the cathode. Thecoating can be composed of, for example, a ternary lithium nitridehaving the formula Li_(x)MN₄, wherein x is 5, 6, or 7 and M is anelement selected from Ta, Nb, W, V, Re, and Mo; a ternary lithiumnitride having the formula Li_(x)MN₂, wherein x is 2 or 3 and furtherwherein, when x is 2, M is selected from Zr, C, and Si, and when x is 3,M is Sc or B; and/or a ternary lithium nitride selected from LiMgN,Li₅Br₂N, Li₁₀BrN₃, Li₄SrN₂, Li₈TeN₂, or a combination thereof. Theelectrolyte can include, for example, a lithium salt in an organicsolvent, such as a carbonate, an ether, or an acetal, or can be a solidelectrolyte, such as a solid polymer electrolyte, an oxide solidelectrolyte, a phosphate solid electrolyte, or a nitride solidelectrolyte. Although, other electrolytes could be used.

Other principal features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the invention will hereafter be describedwith reference to the accompanying drawings.

FIGS. 1A and 1B depict thermodynamic concepts used for screeningcompounds. The stable convex hull is shown with a black dashed line.FIG. 1A illustrates stability for a candidate compound with respect tothe set of nearest-energy competing phases. The competing phases aredetermined by removing the candidate compound and calculating ahypothetical convex hull, which is represented by the red dashed line.FIG. 1B illustrates equilibrium of a compound with Li metal, whichrequires a tie line between the compound and Li metal.

FIG. 2A shows the phase diagram for the Li—Al—O ternary systemcalculated at 400 K using compounds from the OQMD. FIG. 2B shows thephase diagram for the Li—Si—O ternary system calculated at 400 K usingcompounds from the OQMD. FIG. 2C shows the phase diagram for the Li—P—Oternary system calculated at 400 K using compounds from the OQMD. FIG.2D shows the phase diagram for the Li—P—S ternary system calculated at400 K using compounds from the OQMD. In these systems, no ternary phasesexhibit tie lines with lithium metal. When a ternary Li-M-X (X═O, S)phase is combined with an excess of lithium metal, these phase diagramsshow that the phase will react to form Li₂X and a metallic Li-M phase.These metallic phases allow continued electron transport from thelithium anode to the electrolyte and therefore continued reactivity.

DETAILED DESCRIPTION

Materials for coating the metal anode in a high energy battery, anodescoated with the materials, and batteries incorporating the coated anodesare provided. Also provided are batteries that utilize the materials aselectrolytes.

The coatings, which are composed of binary, ternary, and higher ordermetal and/or metalloid oxides, nitrides, fluorides, chlorides, bromides,sulfides, and carbides can reduce the reactions between the electrolyteand active material of a metal anode, such as a lithium anode, a sodiumanode, or a magnesium anode, in a metal battery, thereby improving theperformance of the battery, relative to a battery that employs a bareanode.

A basic embodiment of a battery includes: a cathode; an anode inelectrical communication with the cathode; and an electrolyte disposedbetween the anode and the cathode. If the electrolyte is not a solidelectrolyte, the battery will typically also include a separatordisposed between the anode and the cathode. The batteries includelithium metal batteries, sodium metal batteries, and magnesium metalbatteries.

The electrolytes are ionically conductive materials and may includesolvents, ionic liquids, metal salts, ions such as metal ions orinorganic ions, polymers, ceramics, and other components. An electrolytemay be an organic or inorganic solid or a liquid, such as a solvent(e.g., a non-aqueous solvent) containing dissolved salts.

Example salts that may be included in electrolytes for lithium metalbatteries include lithium salts, such as LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiCIO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(FSO₂)₂N, LiC₄F₉SO₃, LiA1O₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y−1)SO₂), (where χ and y are naturalnumbers), LiCl, LiI, LiNO₃, and mixtures thereof. Non-aqueouselectrolytes can include organic solvents, such as, cyclic carbonates,linear carbonates, fluorinated carbonates, benzonitrile, acetonitrile,tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4methyldioxolane, N,N-dimethylformamide, N,N-dimethylacetamide,N,N-dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,dichloroethane, chlorobenzene, nitrobenzene, diethyleneglycol,dimethylether, and mixtures thereof.

Examples of solid-state electrolytes for lithium metal batteries includesulfide solid electrolytes, such as Li₃PS₄, Li₁₀GeP₂S₁₂, Li₆PS₅Br,Li₇P₂S₈I, Li₃PS₄, Li₁₀SiP₂S₁₂, Li₁₀SnP₂S₁₂, Li₆PS₅Cl,Li_(3.25)Ge_(0.25)P_(0.75)S₄, and Li_(3.4)Si_(0.4)P_(0.6)S₄; oxide solidelectrolytes, such as Li₇La₃Zr₂O₁₂, LiLaTi₂O₆, Li₃PO₄, LiTi₂P₃O₁₂,Li_(1.3)Al_(0.3)Ti_(1.7)(PO₄)₃, Li_(0.34)La_(0.51)TiO_(2.94), andLi_(6.55)La₃Zr₂Ga_(0.15)O₁₂; and nitride solid electrolytes, such asLi₇PN₄. Further examples of sulfide solid-state electrolytes for lithiummetal batteries include mixtures of xLi₂S*(1−x)P₂S₅ where x ranges fromabout 0.7 to about 0.8. Solid polymer electrolytes (SPEs) can also beused.

Examples of electrolytes for sodium metal batteries include NaPF₆(sodium hexafluorophosphate) in glymes (e.g., mono-, di-, andtetraglyme), sodium hexafluorophosphate in glymes, and chloroaluminateionic liquid electrolytes. Magnesium(II) bis(trifluoromethane sulfonyl)amide in triglyme is an example of an electrolyte for a magnesium metalbattery.

The separators are typically thin, porous or semi-permeable, insulatingfilms with high ion permeabilities. The separators can be composed ofpolymers, such as olefin-based polymers (e.g., polyethylene,polypropylene, and/or polyvinylidene fluoride). If a solid-stateelectrolyte, such as a solid polymer electrolyte or solid ceramicelectrolyte, is, the solid-state electrolyte may also act as theseparator and, therefore, no additional separator is needed.

The cathodes are composed of an active cathode material that takes partin an electrochemical reaction during the operation of the battery. Theactive cathode materials for lithium metal batteries may be lithiumcomposite oxides and include layered-type materials, such as LiCoO₂,LiNi_(0.8)Co_(0.15)Al_(0.05)O₂, or Li_(1-x)Ni_(1-y-z)Co_(y)Mn_(z)O₂;olivine-type materials, such as LiFePO₄; spinel-type materials, such asLiMn₂O₄; and similar materials. The spinel-type materials include thosewith a structure similar to natural spinal LiMn₂O₄, that include a smallamount nickel cation in addition to the lithium cation and that,optionally, also include an anion other than manganate. By way ofillustration, such materials include those having the formulaLiNi_((0.5-x))Mn_(1.5)M_(x)O₄, where 0≤x≤0.2 and M is Mg, Zn, Co, Cu,Fe, Ti, Zr, Ru, or Cr. Examples of cathode materials for sodium metalbatteries include Na₃V₂(PO₄)₃, NaMnO₂, NaFePO₄, and Na₂S/activatedcarbon nanofibers. Examples of cathode materials for magnesium metalbatteries include Mo₃S₄, TiSe₂, MgFePO₄F, MgFeSiO₄, MgCo₂O₄, and V₂O₅.

The metal anodes are composed of an active metals (i.e., Li, Na, or Mg),which provides a mobile element and takes part in an electrochemicalreaction during the operation of the battery. The metal anodes can bepure, or substantially pure, metal (i.e., pure or substantially pure Li,Na, or Mg) or alloys of the active metal with one or more additionalmetal elements. In the metal alloys, the alloyed element or elements canbe used to control dendrite formation, mechanical properties, surfacechemistry, voltage, or other materials properties. For example, lithiummay be alloyed with aluminum, indium, or sodium to form a lithium metalanode composed of a lithium metal alloy. Alloyed metal anodes mayinclude a majority or a minority of lithium. In some embodiments of themetal alloys, the active metal makes up a majority (i.e., >50%) of thealloy by weight, while in other embodiments the other metal elementsmake up a majority of the alloy by weight.

The active anode material is at least partially coated with a continuousor discontinuous anode coating of a metal compound and/or metalloidcompound. The coatings allow diffusion of the mobile metal ions (e.g.,Li, Na, or Mg ions) between the anode and electrolyte, while blockingdiffusion of electrons and other species that cause electrochemical orchemical reactions between the anode and the electrolyte. The coatingsmay also limit spatial irregularities at the anode-electrolyte interfacethat can lead to metal dendrites and internal short circuits. Thecoatings thereby create a more stable anode-electrolyte interface toenhance the durability, cycle life, calendar life, power, and/or safetyof the cell. The coating compounds desirably have a high bandgap becausecompounds with higher bandgaps are more likely to maintain electronicinsulation in the harsh chemical environment of a battery. By way ofillustration, some of the coating compounds have bandgaps of at least 1eV. This includes compounds having a bandgap of at least 2 eV, at least3 eV, at least 4 eV, at least 5 eV, at least 6 eV, at least 7 eV, atleast 8 eV, and at least 9 eV.

The coating compounds may be selected from compounds that are stable;exhibit chemical equilibrium with the metal anode; are electronicinsulators; and, desirably do not contain radioactive elements. Themeaning of the terms “stable”, “exhibits chemical equilibrium with themetal anode” and “electronic insulator”, as used herein, are provided inExample 1, which described in detail the methods and calculations thatcan be used to evaluate these properties. Briefly, a coating compound isstable if it has a formation energy lower than any other phase orcombination of phases at the composition of the candidate compound, asidentified using the convex hull methods. A coating compound exhibitschemical equilibrium with a metal anode if it is not consumed to anysignificant extent by a chemical reaction with that anode. This isdetermined by calculating the convex hull for the set of elementsdefined by the compound and the metal anode and determining if a tieline connects the coating compound with the metal of the anode. Theexistence of a tie lie indicates that the compound exhibits stableequilibrium with the metal anode. Finally, a coating compound isconsidered to be an electronic insulator if it has a DFT Kohn-Shambandgap, as tabulated in the Open Quantum Materials Database of at least1.0 eV.

These properties of the coating materials also render the coatingmaterials suitable for use as electrolytes in the batteries. Therefore,the coatings are able to act as an additional electrolyte layer in thebattery. Alternatively, metal batteries can employ the anode coatingmaterials described herein as electrolytes, rather than, or in additionto, anode coatings.

The compounds include binary, ternary and quaternary metal and/ormetalloid oxides, nitrides, halides (e.g., fluorides, chlorides, andbromides), sulfides, and carbides, including compounds in which themetal is an alkali metal, an alkaline earth metal, a transition metal, apost-transition metal, and/or a rare earth metal. Suitable metalsinclude the metal from which the active anode material is composed. Thecoating compounds may be used as pure single phases, combined asatomically mixed phases, or combined as composite mixed phases.

The oxides are compounds of one or more metal and/or metalloid elementsand oxygen. In some embodiments of the coatings, the oxide compoundshave the formula MO, where M is a metal, such as, for example, analkaline earth metal, or a rare earth metal. In some embodiments of thecoatings, the oxide compounds have the formula M₂O₃, wherein M is ametal, such as a rare earth metal. In some embodiment of the coatingsfor lithium anodes, the oxide compounds have the formula LiRO₂, where Ris a rare earth metal. Similarly, in some embodiments of the coatingsfor sodium anodes, the oxide compounds have the formula NaRO₂, where Ris a rare earth metal.

The nitrides are compounds of one or more metal and/or metalloidelements and nitrogen. In some embodiments of the coatings for lithiumanodes, the nitride compounds have the formula Li_(x)MN₄, where x is 5,6, or 7 and M is a metal, such as Ta, Nb, W, V, Re, or Mo.

The sulfides are compounds of one or more metal and/or metalloidelements and sulfur. In some embodiments of the coatings for sodiumanodes, the sulfide compounds have the formula NaRS₂, where R is a rareearth metal.

The chlorides are compounds of one or more metal and/or metalloidelements and chlorine. In some embodiments of the coatings for magnesiumanodes, the chloride compounds have the formula RCl₃, where R is a rareearth metal.

Similarly, the fluorides are compounds of one or more metal and/ormetalloid elements and fluorine; the bromides are compounds of one ormore metal and/or metalloid elements and bromine; and the carbides arecompounds of one or more metal and/or metalloid elements and carbon.

The performance and lifetime of a battery can be still further enhancedif the coating is chemically stable and exhibits chemical equilibriumwith respect to the electrolyte, as well as with the active anode metal.Therefore, in some embodiments of the coated metal anodes, theelectrolyte is selected such that the coating compounds are stable andexhibit chemical equilibrium with respect to the electrolyte. This isdemonstrated in the Example 2, for certain solid-state electrolytes forlithium batteries.

The compounds can be synthesized and formed as coatings using knownmethods for forming coatings on anodes and other substrates. Thecoatings can be formed directly on the anode active material or formedon the electrolyte material and subsequently contacted with the metalanode. For the purposes of this disclosure the latter situation isconsidered a coating on the metal anode by virtue of the contact of thecoating with the surface of a active anode material.

Some embodiments of the coating materials, such as metal oxides andmetalloid oxides and nitrides, including binary and ternary oxides andnitrides, can be applied to the anode active material via atomic layerdeposition (ALD) using known precursors. By way of illustration,compounds of the formula M₂O₃, including compounds where M is a rareearth metal element, can be formed via ALD. Other methods for formingcoatings include the solution phase reaction of a cation precursor withan anion precursor in the presence of the anode active material. Becauseconventional metal anodes take the form of a thin foil, vapor deposition(e.g., chemical vapor deposition, physical vapor deposition, and/orpulsed laser deposition) is well suited for the deposition of the anodecoating materials on the anode substrates. However, powder depositioncan also be used. Some embodiments of the coating materials can beapplied to the anode active material using both external precursors andinternal precursors that are alloyed with the metal anode materials andcan segregate to the surface of the anode to partially form the coating.

It the metal anode is a particulate material, for example a metal ormetal alloy particles embedded in a composite structure, a coated anodecan be made by forming a reaction mixture that includes the anode activematerial particles, a cation precursor, and an anion precursor in asolvent and initiating a precipitation reaction between the cationprecursor and the anion precursor to form the anode coating material onthe anode active material. If the metal anode is in the form of a thinfoil, a mixture of the cation precursor and the anion precursor can beapplied to the surface of the foil and the precipitation reaction can beinitiated there. Alternatively, the anode coating compounds can beformed in the absence of the anode active material and subsequentlycombined with the anode active material to form a composite in which theanode coating materials are in contact with and at least partiallysurround particles of the anode active material. The coating methodscan, optionally, include grinding a mixture of anode coating materialand anode active material and calcining the product.

The coatings may be sufficiently thick that that the bulk of the coatingaway from the interface between the anode active material and the anodecoating material preserves the nominal coating composition. By way ofillustration, some embodiments of the anode coatings have a thickness inthe range from 0.1 to 1000 nm, including thicknesses in the range from0.2 to 500 nm, and from 1 to 200 nm. The amount of anode coatingmaterial based on weight may be, for example, in the range from 0.01 to40% based on the mass of the anode active material. This includes anodecoatings in which the amount of anode coating material is in the rangefrom 0.1 to 30%, based on the mass of the anode active material, andfurther includes anode coatings in which the amount of anode coatingmaterial is in the range from 1 to 15%, based on the mass of the anodeactive material.

The Summary section of this disclosure provides illustrative examples ofsome embodiments of coated lithium metal anodes and lithium batteriesincorporating the coated lithium metal anodes. The immediately followingdescription provides illustrative examples of some embodiments of coatedsodium metal anodes and coated magnesium metal anodes, as well as sodiumand magnesium batteries incorporating the coated metal anodes.

One embodiment of a coated sodium metal anode includes: a sodium metalanode; and a coating on at least a portion of the sodium metal anode,wherein the coating comprises a rare earth metal oxide, and furtherwherein the rare earth metal oxide is stable; exhibits chemicalequilibrium with the sodium metal anode; and is electrically insulating.The coating can be composed of, for example, a rare earth metal oxidehaving the formula R₂O₃ or the formula NaRO₂, where R is a rare earthmetal element. Another embodiment of a coated sodium metal anodeincludes: a sodium metal anode; and a coating on at least a portion ofthe sodium metal anode, wherein the coating comprises a binary metaloxide selected from, for example, CaO, SrO, YbO, BaO, and combinationsthereof, and further wherein the binary metal oxide is stable; exhibitschemical equilibrium with the sodium metal anode; and is electricallyinsulating. Yet another embodiment of a coated sodium metal anodeincludes: a sodium metal anode; and a coating on at least a portion ofthe sodium metal anode, wherein the coating comprises a ternary sodiumoxide selected from, for example, of Na₂ZrO₃, Na₄WO₅, Na₄SiO₄, Na₃BO₃,Na₇Al₃O₈, Na₅TaO₅, Na₅NbO₄, Na₅AlO₄, Na₃ClO, Na₂Hf₂O₅, Na₄Br₂O, andcombinations thereof, and further wherein the ternary sodium oxide isstable; exhibits chemical equilibrium with the sodium metal anode; andis electrically insulating. One embodiment of a sodium batteryincorporating these coated sodium metal anodes includes: the coatedsodium metal anode; a cathode in electrical communication with thecoated sodium metal anode; and an electrolyte disposed between thecoated sodium metal anode and the cathode.

Another embodiment of a coated sodium metal anode includes: a sodiummetal anode; and a coating on at least a portion of the sodium metalanode, wherein the coating comprises a binary metal sulfide selectedfrom, for example, Na₂S, SrS, CaS, YbS, BaS, EuS, and combinationsthereof, and further wherein the binary metal sulfide is stable;exhibits chemical equilibrium with the sodium metal anode; and iselectrically insulating. Another embodiment of a coated sodium metalanode includes: a sodium metal anode; and a coating on at least aportion of the sodium metal anode, wherein the coating comprises aternary sodium sulfide selected from, for example, NaLiS, NaLuS₂,NaErS₂, NaHoS₂, NaYS₂, or NaTmS₂, and combinations thereof, and furtherwherein the ternary sodium sulfide is stable; exhibits chemicalequilibrium with the sodium metal anode; and is electrically insulating.One embodiment of a sodium battery incorporating the coated sodium metalanode includes: the coated sodium metal anode; a cathode in electricalcommunication with the coated sodium metal anode; and an electrolytedisposed between the coated sodium metal anode and the cathode. Theelectrolyte can be, for example, a sulfide solid electrolyte.

Another embodiment of a coated sodium metal anode includes: a sodiummetal anode; and a coating on at least a portion of the sodium metalanode, wherein the coating comprises a metal fluoride, such as LiF, NaF,EuF₂, SrF₂, CaF₂, YbF₂, BaF₂, or a combination thereof, and furtherwherein the metal fluoride is stable; exhibits chemical equilibrium withthe sodium metal anode; and is electrically insulating. One embodimentof a sodium battery incorporating these coated sodium metal anodesincludes: the coated sodium metal anode; a cathode in electricalcommunication with the coated sodium metal anode; and an electrolytedisposed between the coated sodium metal anode and the cathode.

Another embodiment of a coated sodium metal anode includes: a sodiummetal anode; and a coating on at least a portion of the sodium metalanode, wherein the coating comprises a ternary sodium nitride, such asNa₂CN₂, Na₃WN₃, Na₃BN₂, Na₃MoN₃, NaTaN₂, or a combination thereof, andfurther wherein the ternary sodium nitride is stable; exhibits chemicalequilibrium with the sodium metal anode; and is electrically insulating.One embodiment of a sodium battery incorporating these coated sodiummetal anodes includes: the coated sodium metal anode; a cathode inelectrical communication with the coated sodium metal anode; and anelectrolyte disposed between the coated sodium metal anode and thecathode.

One embodiment of a coated magnesium metal anode includes: a magnesiummetal anode; and a coating on at least a portion of the magnesium metalanode, wherein the coating comprises a metal sulfide selected from, forexample, Lu₂MgS₄, MgS, SrS, CaS, YbS, and combinations thereof, andfurther wherein the metal sulfide is stable; exhibits chemicalequilibrium with the magnesium metal anode; and is electricallyinsulating. One embodiment of a magnesium battery incorporating thecoated magnesium metal anode includes: the coated magnesium metal anode;a cathode in electrical communication with the coated magnesium metalanode; and an electrolyte disposed between the coated magnesium metalanode and the cathode. The electrolyte can be, for example, a sulfidesolid electrolyte.

Another embodiment of a coated magnesium metal anode includes: amagnesium metal anode; and a coating on at least a portion of themagnesium metal anode, wherein the coating comprises a ternary magnesiumfluoride or a ternary magnesium chloride, such as KMgF₃, NaMgF₃, RbMgF₃,Mg₃NF₃, CsMgCl₃, Cs₂MgCl₃, K₂MgCl₄, or a combination thereof, andfurther wherein the ternary magnesium fluoride or ternary magnesiumchloride is stable; exhibits chemical equilibrium with the magnesiummetal anode; and is electrically insulating. One embodiment of amagnesium battery incorporating these coated magnesium metal anodesincludes: the coated magnesium metal anode; a cathode in electricalcommunication with the coated magnesium metal anode; and an electrolytedisposed between the coated magnesium metal anode and the cathode.

Another embodiment of a coated magnesium metal anode includes: amagnesium metal anode; and a coating on at least a portion of themagnesium metal anode, wherein the coating comprises a magnesiumnitride, such as Mg₃N₂, MgSiN₂, or a combination thereof, and furtherwherein the magnesium nitride is stable; exhibits chemical equilibriumwith the magnesium metal anode; and is electrically insulating. Oneembodiment of a magnesium battery incorporating these coated magnesiummetal anodes includes: the coated magnesium metal anode; a cathode inelectrical communication with the coated magnesium metal anode; and anelectrolyte disposed between the coated magnesium metal anode and thecathode.

Another embodiment of a coated magnesium metal anode includes: amagnesium metal anode; and a coating on at least a portion of themagnesium metal anode, wherein the coating comprises a ternary magnesiumcarbide, such as MgAl₂C₂, MgB₂C₂, or a combination thereof, and furtherwherein the ternary magnesium carbide is stable; exhibits chemicalequilibrium with the magnesium metal anode; and is electricallyinsulating. One embodiment of a magnesium battery incorporating thesecoated magnesium metal anodes includes: the coated magnesium metalanode; a cathode in electrical communication with the coated magnesiummetal anode; and an electrolyte disposed between the coated magnesiummetal anode and the cathode.

EXAMPLES Example 1: Coatings for Lithium, Sodium, and Magnesium MetalAnodes

In this example, the Open Quantum Materials Database (OQMD) was screenedto identify coatings that exhibit chemical equilibrium with the anodemetals and are electronic insulators. The coatings were ranked accordingto their electronic bandgap. Ninety-two coatings for Li anodes wereidentified, 118 for Na anodes, and 97 for Mg anodes. Only two compoundsthat are commonly studied as Li solid electrolytes passed these screens:Li₃N and Li₇La₃Hf₂O₁₂. Many of the coatings that were identified are newto the battery literature. Notably, the OQMD is compiled from compoundsthat had previously been synthesized, therefore this database can beused as a resource for references describing methods of making compoundsof the type described herein.

The Open Quantum Materials Database was searched to identifyelectronically insulating materials that exhibit stable equilibrium withmetal anodes made of Li, Na, and Mg. It was found that many materialscurrently used in Li batteries as electrode coatings or solidelectrolytes are reactive with Li metal to form unanticipated reactionproducts, including electronically conductive phases that facilitatecontinued transfer of electrons from the anode to the electrolyte.Ninety-two coatings were identified for Li anodes, 118 for Na anodes,and 97 for Mg anodes. These coatings included binary, ternary, andquaternary compounds. For Li anodes, Li-containing ternary coatings wereidentified, including seven oxides and 21 nitrides, but no fluorides orsulfides. For Na anodes, Na-containing ternaries were identified,including 26 oxides, nine nitrides, and six sulfides, but no fluorides.For Mg anodes, Mg-containing ternaries were identified, including fivefluorides, four nitrides, and one sulfide, but no oxides. A variety ofchloride, bromide, and carbide coatings for the anodes were alsoidentified. Only two compounds that are commonly studied as Li solidelectrolytes passed these screens: Li₃N and Li₇La₃Hf₂O₁₂. Many of thecoatings that were identified are new to the battery literature.

Methodology

Calculation of Formation Energies

The Open Quantum Materials Database (OQMD) was screened to identifycoating materials for Li, Na, and Mg metal anodes. The OQMD is apublicly-available database of more than 440,000 compounds containingvarious materials properties, calculated using density functional theory(DFT). (See, Saal, J. E.; Kirklin, S.; Aykol, M.; Meredig, B.;Wolverton, C. Materials Design and Discovery with High-ThroughputDensity Functional Theory: the Open Quantum Materials Database (OQMD).JOM 2013, 65 (11), 1501-1509; Kirklin, S.; Saal, J. E.; Meredig, B.;Thompson, A.; Doak, J. W.; Aykol, M.; Rühl, S.; Wolverton, C. The OpenQuantum Materials Database (OQMD): Assessing the Accuracy of DFTFormation Energies. Nature Publishing Group 2015, 1 (15010), 1-15.) (Thedetails of the various parameters used to perform the DFT calculationsare discussed elsewhere. (See, Kirklin, S.; Saal, J. E.; Meredig, B.;Thompson, A.; Doak, J. W.; Aykol, M.; Rühl, S.; Wolverton, C. The OpenQuantum Materials Database (OQMD): Assessing the Accuracy of DFTFormation Energies. Nature Publishing Group 2015, 1 (15010), 1-15;Grindy, S.; Meredig, B.; Kirklin, S.; Saal, J. E.; Wolverton, C.Approaching Chemical Accuracy with Density Functional Calculations:Diatomic Energy Corrections. Phys. Rev. B 2013, 87 (7), 075150; Perdew,J.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation MadeSimple. Phys. Rev. Lett. 1996, 77 (18), 3865-3868; Blöchl, P. E.Projector Augmented-Wave Method. Phys. Rev. B 1994, 50 (24), 17953;Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the ProjectorAugmented-Wave Method. Phys. Rev. B 1999, 59 (3), 1758; Kresse, G.;Hafner, J. Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B1993, 47 (1), 558-561; Kresse, G.; Hafner, J. Ab InitioMolecular-Dynamics Simulation of theLiquid-Metal-Amorphous-Semiconductor Transition in Germanium. Phys. Rev.B 1994, 49 (20), 14251; Kresse, G.; Furthmüller, J. Efficiency ofAb-Initio Total Energy Calculations for Metals and Semiconductors Usinga Plane-Wave Basis Set. Computational Materials Science 1996, 6, 15-50;Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab InitioTotal-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B1996, 54 (16), 11169; Anisimov, V. I.; Zaanen, J.; Andersen, O. K. BandTheory and Mott Insulators: Hubbard U Instead of Stoner I. Phys. Rev. B1991, 44 (3), 943; Anisimov, V.; Solovyev, I.; Korotin, M.; Czyżyk, M.;Sawatzky, G. Density-Functional Theory and NiO Photoemission Spectra.Phys. Rev. B 1993, 48 (23), 16929; Liechtenstein, A.; Anisimov, V.;Zaanen, J. Density-Functional Theory and Strong Interactions: OrbitalOrdering in Mott-Hubbard Insulators. Phys. Rev. B 1995, 52 (8),5467-5470; Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y.; Humphreys, C.J.; Sutton, A. Electron-Energy-Loss Spectra and the Structural Stabilityof Nickel Oxide: an LSDA+U Study. Phys. Rev. B 1998, 57 (3), 1505-1509.)The formation energy of a compound A_(a)B_(b)C_(c) . . . Z_(z), ΔH_(f)was calculated using

${\Delta\;{H_{f}\left( {A_{a}B_{b}C_{c}\mspace{14mu}\ldots\mspace{14mu} Z_{z}} \right)}} = {{E\left( {A_{a}B_{b}C_{c}\mspace{14mu}\ldots\mspace{14mu} Z_{z}} \right)} - {\sum\limits_{i = A}^{Z}\;{\alpha_{i}\mu_{i}}}}$where E(A_(a)B_(b)C_(c) . . . Z_(z)) is the DFT energy of the compoundfrom the OQMD, α_(i) is the atom fraction of element i in the compound,and μ_(i) is the chemical potential of element i, from the OQMD. Thereference chemical potential of elements whose state at room temperatureis different from that at 0 K (gaseous elements, and elements thatundergo a phase transformation below room temperature) were fit toexperimental formation enthalpies at standard temperature and pressurein the OQMD. (See, Kirklin, S.; Saal, J. E.; Meredig, B.; Thompson, A.;Doak, J. W.; Aykol, M.; Rühl, S.; Wolverton, C. The Open QuantumMaterials Database (OQMD): Assessing the Accuracy of DFT FormationEnergies. Nature Publishing Group 2015, 1 (15010), 1-15.) Further, thefree energies of F, O, Cl, N, and Br were adjusted to their referencestates at 1 atm and 400 K, by adding enthalpy and entropy correctionsfrom the JANAF Thermochemical Tables. (See, Chase, M. W.; Davies, C. A.;Downey, J. F.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. JANAFThermochemical Tables; 1985.) The temperature of 400 K was selected toreflect conditions of vapor deposition on lithium metal and to reflectthe maximum operating temperature of solid state batteries.Screening Criteria

The screening strategy that was used employed four main criteria toidentify potential anode coatings materials: (a) stability, (b)equilibrium with the anode metal, (c) electronic insulation, and (d)lithium content. Additionally, all compounds with radioactive elementswere discarded: Pm, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm,and Bk. The screening criteria are described in detail below.

Stability:

The search for anode coatings was limited to compounds that are stable,because stable compounds are most amenable to synthesis. By definition,a candidate compound is stable if it has a formation energy lower thanany other phase or combination of phases at the composition of thecandidate compound. Stable compounds were identified using the convexhull method, considering all compounds in the OQMD. Stable compoundswere further quantified by calculating a numerical value for stability.The stability of a candidate compound was calculated by taking thenumerical difference between the formation energy of the candidatecompound minus the formation energy of the lowest-energy set ofcompeting phases. The competing phases were determined by consideringall compounds in the OQMD, but removing the candidate compound and otherphases at the candidate compound's composition, and then calculating thelowest-energy set of phases at the candidate compound's composition.Stability was negative for stable compounds, as illustrated in FIG. 1A.

Equilibrium:

In addition to calculating the stability of a compound, it was alsodetermined whether a compound exhibits chemical equilibrium with theanode metals: Li, Na, and Mg. Stability of a compound and equilibrium ofthe compound with a metal anode are two distinct concepts that aresometimes confused. A given solid electrolyte material may be stablewhen synthesized in isolation; however, when such a solid electrolytematerial is combined with a metal anode, it may still be consumed by achemical reaction. Such a material is stable, but it does not exhibitequilibrium with the anode metal. To compute whether a compound exhibitsequilibrium with an anode metal, the convex hull method was again used.For each candidate compound, the convex hull was calculated for the setof elements defined by the compound plus the anode metal. Within thisconvex hull, a tie line connecting the candidate compound with the anodemetal was searched for. The presence of such a tie line was taken as anindication that the candidate compound does exhibit stable equilibriumwith the anode metal. The absence of such a tie line was taken as anindication that the candidate compound does not exhibit stableequilibrium with the anode metal, but rather reacts with the anodemetal. Equilibrium with an anode metal is illustrated in FIG. 1B.

Electronic Insulation:

To identify coatings that are electronically insulating, compounds thatcontain F, O, Cl, N, Br, S, or C were targeted in the search. The DFTKohn-Sham bandgap was considered, as tabulated in the OQMD. (See, Kohn,W.; Sham, L. J. Self-Consistent Equations Including Exchange andCorrelation Effects. Physical Review 1965, 140 (4A), A1133-A1138.)Compounds that exhibit a bandgap above 1.0 eV were screened for. Thissomewhat lenient bandgap value was selected because the Kohn-Shambandgap with the PBE functional systemically underestimates theexperimental bandgap with a mean absolute error of 0.84 eV. (See, Chan,M.; Ceder, G. Efficient Band Gap Prediction for Solids. Phys. Rev. Lett.2010, 105, 196403.) Compounds were ranked according to bandgap becausecompounds with higher bandgaps are more likely to maintain electronicinsulation in the harsh chemical environment of a battery, whilecompounds with smaller bandgaps may become doped and electronicallyconductive.

Lithium Content:

Compounds that contain the anode metal were screened for because allnotable solid electrolytes in the lithium battery literature containlithium sublattices, which enable lithium diffusivity. This requirementfor Li content was relaxed for binary compounds to expand our resultsbeyond the binaries, such as LiF, etc.

During the screening, many compounds were rejected that lackedequilibrium with lithium metal. These rejected compounds included manythat appear in the lithium battery literature as notable solidelectrolytes or electrode coatings. A variety of these compounds wereexamined and their reactions with lithium metal were computed. Reactionproducts were determined by combining each compound with an excess oflithium metal and computing the equilibrium set of phases. The excess oflithium was specified to reflect a lithium metal anode in equilibriumwith a relatively thin coating. Lithium metal anodes are typicallymicrometers in thickness; whereas, anode coatings are typicallynanometers in thickness. Li₁₀GeP₂S₁₂ and LiLaTi₂O₆ were not available inthe OQMD, so for these reactions, formation energies were used from theMaterials Project. (See, Jain, A.; Ong, S. P.; Hautier, G.; Chen, W.;Richards, W. D.; Dacek, S.; Cholia, S.; Gunter, D.; Skinner, D.; Ceder,G.; et al. Commentary: the Materials Project: a Materials GenomeApproach to Accelerating Materials Innovation. APL Mater. 2013, 1,011002; Ong, S. P.; Wang, L.; Kang, B.; Ceder, G. Li—Fe—P—O2 PhaseDiagram From First Principles Calculations. Chem. Mater. 2008, 20,1798-1807; Jain, A.; Hautier, G.; Ong, S. P.; Moore, C. J.; Fischer, C.C.; Persson, K. A.; Ceder, G. Formation Enthalpies by Mixing GGA andGGA+U Calculations. Phys. Rev. B 2011, 84, 045115.)

Results and Discussion

It was found that many solid electrolyte and electrode coating materialsin the lithium battery literature, including oxides and sulfides, arereactive with lithium metal. Table 1 lists these reactions andcorresponding reaction energies, which range from −18 to −714 meV/atom.The list includes two sulfide compounds, which exhibit the two highestreaction energies. Compounds that are reactive with lithium metalinclude notable solid electrolytes such as Li₇La₃Zr₂O₁₂ (LLZO),LiLaTi₂O₆ (LLTO), and Li₁₀GeP₂S₁₂ (LGPS) as well as notable electrodecoatings such as Al₂O₃, Li₃PO₄, and LiAlO₂. Each compound yields two orthree reaction products including Li₂O for oxides and Li₂S for sulfides.Besides Li₂O or Li₂S, the remaining reaction products typically includeat least one phase that is electronically conductive. Theseelectronically conductive phases, when formed on the anode surface,facilitate electron transfer from the anode to the electrolyte. Thiselectron transfer allows continued reactivity and prevents passivationof the anode/electrolyte interface. Only one compound in Table 1, LLZO,yields reaction products that are all electronically insulating andtherefore capable of passivating the surface of lithium metal. This isconsistent with experiments reported by Luntz et al. A list of solidelectrolytes was considered, including LLZO, LGPS, lithium phosphorousoxynitride (LiPON), and Li₃ClO and it was found that only LLZO “appearsto be chemically stable to reduction by lithium metal.” (See, Luntz, A.C.; Voss, J.; Reuter, K. Interfacial Challenges in Solid-State Li IonBatteries. J. Phys. Chem. Lett. 2015, 6, 4599-4604.) The results supportand clarify this experimental finding, showing that LLZO is resistant toreduction by lithium metal due to passivation. However, anode coatingsat the interface between lithium metal and LLZO can improve theproperties of the interface and improve battery performance.

TABLE 1 Compounds that are commonly tested as electrode coatings andsolid electrolyes in lithium batteries often react with lithium metalanodes. The corresponding reactions and reaction energies (meV/atom) arelisted. Most reaction products include electronically conductive phases,which can hinder passivation of the lithium metal surface and facilitatefurther reactivity. The existence of such conductive reaction productsis indicated in the last column. Compound Reaction ΔE^(rxn) ConductiveLi₃PS₄ Li₃PS₄ + 8*Li → 4*Li₂S + Li₃P −714 Yes Li₁₀GeP₂S₁₂ Li₁₀GeP₂S₁₂ +23.75*Li → 12*Li₂S + −642 Yes 2*Li₃P + 0.25*Li₁₅Ge₄ ZnO ZnO + 3*Li →Li₂O + LiZn −613 Yes Li₃PO₄ Li₃PO₄ + 8*Li → 4*Li₂O + Li₃P −338 Yes SiO₂SiO₂ + 41/5*Li → 2*Li₂O + ⅕*Li₂₁Si₅ −332 Yes LiLaTi₂O₆ LiLaTi₂O₆ +14/3*Li → 17/6*Li₂O + LaTiO₃ + −164 Yes ⅙*Ti₆O Al₂O₃ Al₂O₃ + 10.5*Li →3*Li₂O + 0.5*Li₉Al₄ −152 Yes Li₇La₃Zr₂O₁₂ Li₇La₃Zr₂O₁₂ + 2*Li →4.5*Li₂O + −138 No (LLZO) 0.5*La₂O₃ + 2*LaZrO₃ Li₄SiO₄ Li₄SiO₄ + 41/5*Li→ 4*Li₂O + ⅕*Li₂₁Si₅ −105 Yes LiAlO₂ LiAlO₂ + 21/4*Li → 2*Li₂O +¼*Li₉Al₄ −62 Yes MgO MgO + 7*Li → Li₂O + Li₅Mg −18 Yes

The tendency of oxide and sulfide compounds to react with lithium metalto form Li₂O or Li₂S highlights the difficulty in finding compounds thatexhibit equilibrium with lithium metal. This tendency is illustrated bythe Li—Al—O, Li—Si—O, Li—P—O, and Li—P—S phase diagrams shown in FIGS.2A, 2B, 2C, and 2D, respectively. These phase diagrams contain a varietyof ternary phases, which might otherwise have good properties forcoatings, except that none of these phases share a tie line with Limetal. In these phase diagrams, Li metal shares tie lines only with Li₂Oor Li₂S plus metallic phases, which prevent passivation.

Ninety-two promising coatings for Li metal anodes were identified, aswell as 118 promising coatings for Na metal anodes, and 97 promisingcoatings for Mg anodes. These coatings include binary, ternary, andquaternary compounds. The tally of coatings is resolved for eachanode/anion pair in Table 2. At least one binary coating passed thescreens for each anode/anion pair. Ternary compounds passed the screensfor all pairs except Li/F, Na/F, Li/S, and Mg/O. Quaternary compoundspassed the screens only for Li/O, Li/N, Li/C, Na/O, and Na/N. Somecompounds that passed the screens contained multiple anions from thelist, including six coatings identified for Li metal, six coatingsidentified for Na metal, and one coating identified for Mg metal.

Nine pentary compounds passed the screens across the Li/N, Li/Br, Li/C,and Na/O pairs, but all of these pentaries had low concentrations of Liand Na, for example, LiEu₂CBr₃N₂ or KNaLaTaO₅. Therefore, an additionalscreen was imposed to exclude compounds with five or more elements.

TABLE 2 Tally of compounds that were identified as promising coatingsfor Li, Na, and Mg metal anodes. The tally is resolved according to theanode metal, the anion, and the number of elements in the compound.Anions Anodes F O Cl N Br S C Li Binaries 5 16 9 4 9 6 1 Ternaries 0 7 121 2 0 2 Quaternaries 0 4 0 10 0 0 1 Na Binaries 7 24 5 10 5 7 3Ternaries 0 26 1 9 1 6 1 Quaternaries 0 13 0 6 0 0 0 Mg Binaries 11 1421 4 18 11 2 Ternaries 5 0 4 4 1 1 2 Quaternaries 0 0 0 0 0 0 0

For Li metal anodes, Tables 3-9 list the binary and ternary compoundsthat passed the screens containing F, O, Cl, N, Br, S, and C anions,respectively. Table 10 lists all quaternary compounds for lithium metalanodes, which included O, N, and C anions. Across all 92 compounds thatpassed the screens for Li anodes, only two compounds are commonlystudied as solid electrolytes: Li₃N and Li₇La₃Hf₂O₁₂. Li₃N is known toexhibit high Li diffusivity. However, the low bandgap for Li₃N (1.2 eVby DFT, 2.2 eV by experiment) may be susceptible to electronic doping ona Li metal anode. Furthermore, Li₃N is not chemically stable with manyelectrolytes. Li₇La₃Hf₂O₁₂ is a lesser-known member of the garnetfamily, which also contains compounds such as Li₇La₃Zr₂O₁₂,Li₅La₃Nb₂O₁₂, and Li₅La₃Ta₂O₁₂, which have received more attention inthe solid electrolyte literature. The finding of equilibrium with Limetal for the garnet Li₇La₃Hf₂O₁₂ is somewhat surprising, given that thebetter-studied Li₇La₃Zr₂O₁₂ garnet does not exhibit equilibrium with Limetal. The competing phases for Li₇La₃Hf₂O₁₂ are Li₂O, La₂O₃, andLi₂HfO₃. All three of these competing phases also exhibit equilibriumwith Li metal, providing additional assurance for Li₇La₃Hf₂O₁₂ as arobust coating on Li metal. Also proposed is a Li₇La₃M₂O₁₂ (M=Hf, Zr)garnet solid electrolyte that is rich in Hf near the anode for chemicalequilibrium but rich in Zr away from the anode for greater Liconductivity.

According to the findings, Li₇La₃Hf₂O₁₂ qualifies as a coating andtherefore may be employed as a solid electrolyte in direct contact withLi metal without the need for any other intervening anode coating.However, for other electrolytes that lack equilibrium with Li metal,such as those listed in Table 1 as well as various liquid electrolytes,an intervening anode coating was needed to prevent electrochemicalreduction of the electrolyte. The compounds identified in Tables 3-10can be employed as anode coatings to stabilize such anode/electrolyteinterfaces.

Throughout the 92 compounds identified as coatings for Li metal anodes,a few classes of compounds can be distinguished. Within the 16 binaryoxides, 11 are members of R₂O₃ where R is a rare earth elementsincluding Y, Lu, Dy, Tm, Ho, Er, Gd, Nd, Sm, Pr, and La. CaO is uniqueamong the oxide coatings for lithium metal in that it contains onlylow-cost and non-toxic elements. Within the seven ternary oxides, sixare members of LiRO₂, where R is a rare earth element including Gd, Dy,Tb, Ho, Er, and Sc. The remaining ternary oxide is Li₂HfO₃, whichbelongs to the set of competing phases for the garnet Li₇La₃Hf₂O₁₂.Within the 21 ternary nitrides, six are members of Li_(x)MN₄, where x=5,6, or 7 and M is a transition metal including Ta, Nb, W, V, Re, and Mo.These nitride compounds are similar in composition to Li₃N, which isknown to have good Li conductivity. However, these compounds have largerbandgaps than Li₃N, which may improve their ability to block electrontransfer. And, unlike Li₃N, many of these compounds exhibit stableequilibrium with oxide solid electrolytes.

Tables 3-10 list coatings for Li metal anodes. Tables 3-9 list binaryand ternary coatings containing F, O, Cl, N, Br, S, and C anions,respectively. Table 10 lists quaternary coatings, which include N, O,and C anions. Electronic bandgaps and stabilities are reported in eV.Stabilities are calculated with respect to the nearest-energy set ofcompeting phases. Space group and prototype structure are also listed.

TABLE 3 Fluoride binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLiF 9.56 −1.050 LiF₂—Li₃F₂ Fm3m B1 EuF₂ 7.94 −0.925 Eu₂F₃—EuF₃ Fm3m CaF₂SrF₂ 7.43 −1.232 SrF—SrF₃ Fm3m CaF₂ CaF₂ 7.41 −0.965 CaF₃—Ca₂F₃ R3m NoneYbF₂ 7.31 −1.287 YbF₃—YbF P4₂/mnm C4

TABLE 4 Oxide binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsBeO 7.90 −1.584 Be—Be₂O₃ P6₃mc B4 Li₂O 5.08 −0.657 LiO—Li₃O R3m NoneY₂O₃ 4.37 −0.823 YO₂—Y₄O₅ Ia3 Mn₂O₃ Lu₂O₃ 4.22 −1.056 Lu₄O₅—O₂ Ia3 Mn₂O₃Dy₂O₃ 4.17 −0.989 Dy₄O₅—O₂ Ia3 Mn₂O₃ Tm₂O₃ 4.16 −0.859 TmO₂—Tm₄O₅ I2₁₃Sm₂O₃ Ho₂O₃ 4.14 −1.011 Ho₄O₅—O₂ Ia3 Mn₂O₃ Er₂O₃ 4.12 −1.016 Er₄O₅—O₂Ia3 Mn₂O₃ Gd₂O₃ 4.08 −0.969 Gd₄O₅—O₂ Ia3 Mn₂O₃ Nd₂O₃ 4.05 −0.571NdO₂—NdO Ia3 Mn₂O₃ Sm₂O₃ 3.98 −0.824 Sm₄O₅—SmO₂ Ia3 Mn₂O₃ Pr₂O₃ 3.91−0.419 Pr₇O₁₂—PrO Ia3 Mn₂O₃ La₂O₃ 3.81 −1.134 LaO—LaO₃ Ia3 Mn₂O₃ CaO3.75 −1.134 Ca₂O₃—Ca₂O Fm3m B1 YbO 3.52 −0.950 Yb₄O₅—Yb₃O₂ Fm3m B1 EuO2.81 −0.797 Eu₂O—Eu₃O₄ Fm3m B1 Ternary Lithium-Containing CompoundsLiGdO₂ 4.90 −0.004 Li₂O—Gd₂O₃ Pnma SrZnO₂ Li₂HfO₃ 4.86 −0.096Li₂O—Li₈Hf₄O₁₁—Li₆Hf₄O₁₁ C2/m None LiDyO₂ 4.83 −0.012 Li₂O—Dy₂O₃ PnmaSrZnO₂ LiTbO₂ 4.83 −0.008 Li₂O—Tb₂O₃ Pnma SrZnO₂ LiHoO₂ 4.51 −0.001Li₂O—Ho₂O₃ P2₁/c YLiO₂ LiErO₂ 4.51 −0.011 Li₂O—Er₂O₃ P2₁/c YLiO₂ LiScO₂4.32 −0.090 Li₂O—Sc₂O₃ I4₁/amd LiFeO₂- alpha

TABLE 5 Chloride binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLiCl 6.25 −0.772 Li₃Cl₂—LiCl₂ F4 ₃m B3 BaCl₂ 5.69 −0.648 BaCl₃—Ba₂Cl₃Fm3m CaF₂ YbCl₂ 5.63 −0.250 Yb₆Cl₁₃—Yb P4₂/mnm C4 SrCl₂ 5.53 −0.962SrCl—SrCl₃ Fm3m CaF₂ KCl 5.30 −0.732 KCl₂—K₃Cl₂ Fm3m B1 EuCl₂ 5.19−0.837 EuCl—EuCl₃ Pnma PbCl₂ NaCl 5.18 −0.727 NaCl₂—Na₃Cl₂ Fm3m B1 CsCl5.08 −0.629 Cs₃Cl₂—CsCl₂ Fm3m B1 RbCl 4.98 −0.715 Rb₃Cl₂—Cl₂ R3m L1₁Ternary Lithium-Containing Compounds Li₄NCl 2.02 −0.007 Li₃N—Li₅NCl₂ R3mNone

TABLE 6 Nitride binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsAlN 4.34 −1.275 Al₃N—N₂ P6₃mc B4 Be₃N₂ 3.52 −0.710 Be₂N—N₂ Ia3 Mn₂O₃ LaN1.29 −0.647 La₂N—N₂ P6₃mc B4 Li₃N 1.22 −0.319 Li—N₂ P6/ Li₃N mmm TernaryLithium-Containing Compounds Li₂CN₂ 4.11 −0.404 Li₃N—LiCN—N₂ I4/ Nonemmm Li₂SiN₂ 4.07 −0.131 Li₃N—LiSi₂N₃ Pbca None Li₃BN₂ 3.67 −0.176Li₃N—BN P2₁/c Na₃BN₂ Li₇TaN₄ 3.51 −0.079 Li₃N—Li₄TaN₃ Pa3 Li₇TaN₄Li₇NbN₄ 3.51 −0.278 Li₃N—Nb₅N₆—N₂ Pa3 Li₇TaN₄ Li₆WN₄ 3.38 −0.485Li₃N—W—N₂ P4₂/ Li₆ZnO₄ nmc Li₇VN₄ 3.32 −0.293 Li₃N—VN—N₂ Pa3 Li₇TaN₄LiBeN 3.00 −0.115 Li₃N—Be₃N₂ P2₁/c None Li₅ReN₄ 2.92 −0.365 Li₃N—Re—N₂Pmmn Li₅AlO₄ Li₆MoN₄ 2.78 −0.325 Li₃N—LiMoN₂—N₂ P4₂/ Li₆ZnO₄ nmc Li₈TeN₂2.63 −0.025 Li₃N—Li₂Te I4₁md None LiMgN 2.56 −0.058 Li₃N—Mg₃N₂ Pnma NoneLi₅Br₂N 2.46 −0.008 LiBr—Li₁₀BrN₃ Immm None Li₃ScN₂ 2.44 −0.049 Li₃N—ScNIa3 AlLi₃N₂ Li₄NCl 2.02 −0.007 Li₃N—Li₅NCl₂ R3m None Li₄HN 1.98 −0.002Li₃N—LiH I4₁/a CaWO₄ Li₈SeN₂ 1.89 −0.001 Li₃N—Li₂Se I4₁md None Li₂ZrN₂1.73 −0.221 Li₃N—Zr₃N₄ P3m1 La₂O₃ LiCaN 1.64 −0.049 Li₃N—Ca₃N₂ Pnma NoneLi₁₀BrN₃ 1.54 −0.005 Li₃N—Li₅Br₂N P6m2 None SrLi₄N₂ 1.10 −0.016Li₃N—SrLiN I4₁/amd Li₄SrN₂

TABLE 7 Bromide binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLiBr 5.15 −0.673 LiBr₂—Li₃Br₂ F4 ₃m B3 YbBr₂ 4.80 −0.783 YbBr₃—YbBr PnnmNone SrBr₂ 4.72 −0.827 SrBr₃—SrBr Pnma PbCl₂ BaBr₂ 4.48 −0.557Ba₂Br₃—BaBr₃ Pnma PbCl₂ KBr 4.45 −0.622 K₃Br₂—KBr₂ Fm3m NaCl RbBr 4.42−0.613 Rb₃Br₂—RbBr₂ Fm3m B1 CsBr 4.41 −0.543 CsBr₃—Cs₃Br₂ Fm3m B1 EuBr₂4.40 −0.812 EuBr—EuBr₃ P4/n SrBr₂ NaBr 4.36 −0.639 NaBr₃—Na₃Br₂ Fm3m B1Ternary Lithium-Containing Compounds Li₅Br₂N 2.46 −0.008 LiBr—Li₁₀BrN₃Immm None Li₁₀BrN₃ 1.54 −0.005 Li₃N—Li₅Br₂N P6m2 None

TABLE 8 Sulfide binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLi₂S 3.66 −0.561 Li₃S—LiS Fm3m None SrS 2.57 −0.666 SrS₂—Sr₃S₂ Fm3m B1CaS 2.50 −0.988 Ca₂S—Ca₂S₃ Fm3m B1 YbS 2.33 −0.431 Yb₃S₂—Yb₇S₈ Fm3m NoneBaS 2.24 −0.594 Ba₂S—Ba₂S₃ Fm3m B1 EuS 2.07 −0.701 Eu₂S—Eu₃S₄ Fm3m NaCl

TABLE 9 Carbide binary and ternary coatings for Li metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsBe₂C 1.41 −0.234 Be—C Fm3m CaF₂ Ternary Lithium-Containing CompoundsLi₂CN₂ 4.11 −0.404 Li₃N—LiCN—N₂ I4/mmm None LiBC 1.22 −0.270 LiB₆C—C—LiP6₃/mmc KZnAs

TABLE 10 Quaternary coatings for lithium metal anodes. Band Space GapStability Competing Phases Group Prototype Oxide Compounds Li₇La₃Hf₂O₁₂4.68 −0.006 Li₂O—Li₂HfO₃—La₂O₃ I4₁/acd None Li₁₆Nb₂N₈O 3.73 −0.004Li₂O—Li₇NbN₄ R3 Li₁₆Ta₂N₈O Li₁₆Ta₂N₈O 3.53 −0.005 Li₂O—Li₇TaN₄ R3Li₁₆Ta₂N₈O LiSmEu₂O₄ 3.05 −0.006 Li₂O—EuO—Sm₂O₃ Pnma None NitrideCompounds Li₁₆Nb₂N₈O 3.73 −0.004 Li₂O—Li₇NbN₄ R3 Li₁₆Ta₂N₈O Li₁₆Ta₂N₈O3.53 −0.005 Li₂—Li₇TaN₄ R3 Li₁₆Ta₂N₈O Li₅La₅Si₄N₁₂ 2.68 −0.046LaN—La₅Si₃N₉—Li₂SiN₂ P4b2 None Li₄Ca₃Si₂N₆ 2.58 −0.054Li₂SiN₂—LiCaN—Ca₅Si₂N₆ C2/m None Sr₄LiB₃N₆ 2.47 −0.241BN—Sr₂N—Li₃BN₂—SrN Im3m Sr₉B₆N₁₂ Li₅Ce₅Si₄N₁₂ 2.43 −0.039Li₂SiN₂—CeN—Ce₃Si₆N₁₁ P4b2 None LiEu₄B₃N₆ 2.40 −0.058 Li₃BN₂—Eu₃B₂N₄Im3m Sr₉B₆N₁₂ LiCa₄B₃N₆ 2.40 −0.081 Ca₃BN₃—Li₃BN₂—BN Im3m Sr₉B₆N₁₂Sr₃Li₄Si₂N₆ 2.22 −0.062 SrLiN—SrLi₂Si₂N₄ C2/m None SrLi₂CrN₃ 1.09 −0.265Li₃N—Sr₃CrN₃—CrN—N₂ Pbca TeCl₂SSeN₂ Carbide Compounds LiCa₂HC₃ 1.50−0.140 Ca—CaH₂—Li₂Ca—C P4/mbm None

Tables 11-18 list coatings for Na metal anodes. Tables 11-17 list binaryand ternary coatings containing F, O, Cl, N, Br, S, and C anions,respectively. Table 18 lists quaternary coatings, which include N and Oanions. Electronic bandgaps and stabilities are reported in eV.Stabilities are calculated with respect to the nearest-energy set ofcompeting phases. Space group and prototype structure are also listed.

TABLE 11 Fluoride binary and ternary coatings for Na metal anodes.Competing Space Band Gap Stability Phases Group Prototype BinaryCompounds LiF 9.56 −1.050 LiF₂—Li₃F₂ Fm3m B1 EuF₂ 7.94 −0.925 Eu₂F₃—EuF₃Fm3m CaF₂ SrF₂ 7.43 −1.232 SrF—SrF₃ Fm3m CaF₂ CaF₂ 7.41 −0.965CaF₃—Ca₂F₃ R3m None YbF₂ 7.31 −1.287 YbF₃—YbF P4₂/mnm C4 BaF₂ 7.05−0.846 BaF₃—Ba₂F₃ Fm3m None NaF 6.65 −0.908 Na₃F₂—NaF₂ Fm3m B1

TABLE 12 Oxide binary and ternary coatings for Na metal anodes.Competing Space Band Gap Stability Phases Group Prototype BinaryCompounds BeO 7.90 −1.584 Be—Be₂O₃ P6₃mc B4 Li₂O 5.08 −0.657 LiO—Li₃OR3m None MgO 4.97 −1.010 Mg₂O—Mg₄O₅ Fm3m B1 Y₂O₃ 4.37 −0.823 Y₄O₅—YO₂Ia3 Mn₂O₃ HfO₂ 4.29 −0.784 Hf₂O₃—Hf₂O₅ P2₁/c ZrO₂ Lu₂O₃ 4.22 −1.056Lu₄O₅—O₂ Ia3 Mn₂O₃ Dy₂O₃ 4.17 −0.989 Dy₄O₅—O₂ Ia3 Mn₂O₃ Tm₂O₃ 4.16−0.859 TmO₂—Tm₄O₅ I2₁₃ Sm₂O₃ Ho₂O₃ 4.14 −1.011 Ho₄O₅—O₂ Ia3 Mn₂O₃ Sc₂O₃4.12 −0.840 ScO₂—Sc₄O₅ Ia3 Mn₂O₃ Er₂O₃ 4.12 −1.016 Er₄O₅—O₂ Ia3 Mn₂O₃Tb₂O₃ 4.09 −0.488 TbO—Tb₇O₁₂ Ia3 Mn₂O₃ Gd₂O₃ 4.08 −0.969 Gd₄O₅—O₂ Ia3Mn₂O₃ Nd₂O₃ 4.05 −0.571 NdO₂—NdO Ia3 Mn₂O₃ Sm₂O₃ 3.98 −0.824 Sm₄O₅—SmO₂Ia3 Mn₂O₃ Pr₂O₃ 3.91 −0.419 Pr₇O₁₂—PrO Ia3 Mn₂O₃ Ce₂O₃ 3.81 −0.409Ce₇O₁₂—CeO Ia3 Mn₂O₃ La₂O₃ 3.81 −1.134 LaO—LaO₃ Ia3 Mn₂O₃ CaO 3.75−1.134 Ca₂O₃—Ca₂O Fm3m B1 SrO 3.52 −0.801 Sr₃O₂—Sr₄O₅ Fm3m B1 YbO 3.52−0.950 Yb₃O₂—Yb₄O₅ Fm3m B1 EuO 2.81 −0.797 Eu₂O—Eu₃O₄ Fm3m B1 Na₂O 2.22−0.406 NaO—Na₃O Fm3m CaF₂ BaO 2.10 −0.710 Ba₄O₅—Ba₂O Fm3m B1 TernarySodium-Containing Compounds Na₂ZrO₃ 4.51 −0.110 Na₈Zr₄O₁₁—Na₆Zr₂O₇—ZrO₂C2/m None NaYO₂ 4.49 −0.099 Na₂O—Y₂O₃ C2/c None NaErO₂ 4.44 −0.115Na₂O—Er₂O₃ C2/c NaErO₂ NaTbO₂ 4.17 −0.103 Na₂O—Tb₂O₃ I4₁/amd LiFeO₂-alpha NaGdO₂ 4.13 −0.102 Na₂O—Gd₂O₃ I4₁/amd LiFeO₂- alpha NaAlO₂ 4.13−0.117 Na₇Al₃O₈—Al₂O₃ Pna2₁ NaFeO₂ Na₆Be₈O₁₁ 3.95 −0.002 Na₂BeO₂—BeO P1None NaNdO₂ 3.72 −0.089 Na₂O—Nd₂O₃ I4₁/amd LiFeO₂- alpha NaScO₂ 3.70−0.093 Na₂O—Sc₂O₃ I4₁/amd None Na₄WO₅ 3.67 −0.100 Na₂O—Na₂WO₄ P1 Li₄TeO₅Na₄SiO₄ 3.60 −0.091 Na₂SiO₃—Na₈SiO₆ P1 None NaPrO₂ 3.60 −0.082Na₂O—Pr₂O₃ I4₁/amd LiFeO₂- alpha Na₄TiO₄ 3.59 −0.112 Na₂O—Na₂TiO₃ P1Na₄SiO₄ Na₃BO₃ 3.33 −0.072 Na₂O—Na₄B₂O₅ P2₁/c None Na₂BeO₂ 3.11 −0.045Na₂O—Na₆Be₈O₁₁ P2₁ None Na₇Al₃O₈ 2.98 −0.007 NaAlO₂—Na₁₇Al₅O₁₆ P1 NoneNa₅TaO₅ 2.87 −0.148 Na₂O—NaTaO₃ C2/c Na₅NbO₅ Na₅NbO₅ 2.81 −0.158Na₂O—NaNbO₃ C2/c Na₅NbO₅ Na₅AlO₄ 2.66 −0.005 Na₂O—Na₁₇Al₅O₁₆ Pmmn NoneNa₁₇Al₅O₁₆ 2.56 −0.007 Na₅AlO₄—Na₇Al₃O₈ Cm None Na₄I₂O 2.44 −0.030Na₂O—NaI I4/mmm K₂MgF₄ Na₅GaO₄ 2.40 −0.040 Na₂O—Na₃₉Ga₈O₃₂—NaGa₄ PbcaNone Na₃ClO 2.25 −0.003 NaCl Pm3m CaTiO₃ Na₂Hf₂O₅ 2.17 −0.011 Na₂O—HfO₂P4/mmm defect_perov skite Na₄Br₂O 2.14 −0.019 NaBr I4/mmm K₂MgF₄ NaNbO₂1.53 −0.137 NaNbO₃—Nb—Na₅NbO₅ P6₃/mmc None

TABLE 13 Chloride coatings for sodium metal anodes. Competing Space BandGap Stability Phases Group Prototype Binary Compounds YbCl₂ 5.63 −0.250Yb₆Cl₁₃—Yb P4₂/mnm C4 EuCl₂ 5.19 −0.837 EuCl—EuCl₃ Pnma PbCl₂ NaCl 5.18−0.727 NaCl₂—Na₃Cl₂ Fm3m B1 CsCl 5.08 −0.629 Cs₃Cl₂—CsCl₂ Fm3m B1 RbCl4.98 −0.715 Rb₃Cl₂—Cl₂ R3m L1₁ Ternary Sodium-Containing CompoundsNa₃ClO 2.25 −0.003 NaCl Pm3m CaTiO₃

TABLE 14 Nitride binary and ternary coatings for Na metal anodes. BandSpace Gap Stability Competing Phases Group Prototype Binary Compounds BN4.38 −1.071 B₁₃N₂—N₂ P6₃/ BN mmc AlN 4.34 −1.275 Al₃N—N₂ P6₃mc B4 Be₃N₂3.52 −0.710 Be₂N—N₂ Ia3 Mn₂O₃ GaN 1.99 −0.382 Ga—N₂ P6₃mc B4 Mg₃N₂ 1.78−0.351 Mg₂N—N₂ Ia3 Mn₂O₃ LaN 1.29 −0.647 La₂N—N₂ P6₃mc B4 Ca₃N₂ 1.26−0.091 Ca₂N—N₂ Ia3 Mn₂O₃ Li₃N 1.22 −0.319 Li—N₂ P6/ Li₃N mmm Hf₃N₄ 1.17−0.071 HfN—N₂ I4 ₃d Th₃P₄ Zr₃N₄ 1.04 −0.009 ZrN—N₂ Pnma None TernarySodium-Containing Compounds NaPN₂ 4.87 −0.259 NaP₄N₇—Na₃P—N₂ I4 ₂d KCoO₂NaSi₂N₃ 4.48 −0.186 Na—Si₃N₄—N₂ Cmc2₁ Na₂SiO₃ Na₂CN₂ 3.35 −0.337Na—NaCN—N₂ C2/m K₂ Na₄ReN₃ 2.48 −0.255 Na—Re—N₂ Cc Na₄FeO₃ NaH₂N 2.13−0.122 NaH—H₃N—N₂ Fddd NaNH₂ Na₃WN₃ 1.85 −0.429 Na—W—N₂ Cc Na₃MoN₃Na₃BN₂ 1.85 −0.114 Na—BN—N₂ P2₁/c Na₃BN₂ Na₃MoN₃ 1.58 −0.280 Na—MoN—N₂Cc Na₃MoN₃ NaTaN₂ 1.51 −0.188 Na—NaTa₃N₅—N₂ R3m NaCrS₂

TABLE 15 Bromide binary and ternary coatings for Na metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsKBr 4.45 −0.622 K₃Br₂—KBr₂ Fm3m NaCl RbBr 4.42 −0.613 Rb₃Br₂—RbBr₂ Fm3mB1 CsBr 4.41 −0.543 CsBr₃—Cs₃Br₂ Fm3m B1 EuBr₂ 4.40 −0.812 EuBr—EuBr₃P4/n SrBr₂ NaBr 4.36 −0.639 NaBr₃—Na₃Br₂ Fm3m B1 TernarySodium-Containing Compounds Na₄Br₂O 2.14 −0.019 NaBr I4/mmm K₂MgF₄

TABLE 16 Sulfide binary and ternary coatings for Na metal anodes.Competing Space Band Gap Stability Phases Group Prototype BinaryCompounds Li₂S 3.66 −0.561 Li₃S—LiS Fm3m None Na₂S 2.63 −0.377 Na₃S—NaSFm3m CaF₂ SrS 2.57 −0.666 SrS₂—Sr₃S₂ Fm3m B1 CaS 2.50 −0.988 Ca₂S—Ca₂S₃Fm3m B1 YbS 2.33 −0.431 Yb₃S₂—Yb₇S₈ Fm3m None BaS 2.24 −0.594 Ba₂S—Ba₂S₃Fm3m B1 EuS 2.07 −0.701 Eu₂S—Eu₃S₄ Fm3m NaCl Ternary Sodium-ContainingCompounds NaLiS 3.40 −0.005 Li₂S P4/nmm Cu₂Sb NaLuS₂ 2.55 −0.153Na₂S—Lu₂S₃ R3m NaCrS₂ NaErS₂ 2.47 −0.159 Na₂S—Er₂S₃ R3m NaCrS₂ NaHoS₂2.42 −0.154 Na₂S—Ho₂S₃ R3m NaCrS₂ NaYS₂ 2.40 −0.152 Na₂S—Y₂S₃ R3m NaCrS₂NaTmS₂ 2.39 −0.153 Na₂S—Tm₂S₃ R3m NaCrS₂

TABLE 17 Carbide binary and ternary coatings for Na metal anodes.Competing Space Band Gap Stability Phases Group Prototype BinaryCompounds SiC 2.15 −0.209 C—Si P6₃mc SiC Al₄C₃ 1.47 −0.098 C—Al R3m NoneBe₂C 1.41 −0.234 Be—C Fm3m CaF₂ Ternary Sodium-Containing CompoundsNa₂CN₂ 3.35 −0.337 Na—NaCN—N₂ C2/m K₂

TABLE 18 Quaternary coatings for sodium metal anodes. Band Space GapStability Competing Phases Group Prototype Oxide Compounds NaLi₂PO₄ 5.65−0.054 Na₂O—Na₄P₂O₇—Li₃PO₄ Pnma Li₃PO₄ NaLi₃SiO₄ 5.28 −0.007Na₄SiO₄—Li₄SiO₄ I4₁/a None Na₃Ca₂TaO₆ 4.39 −0.073 NaTaO₃—CaO—Na₅TaO₅Fddd None Na₂MgSiO₄ 4.15 −0.018 MgO—Na₂SiO₃ Pna2₁ Na₂ZnSiO₄ NaLa₂TaO₆4.12 −0.017 La₃TaO₇—Na₅TaO₅—NaTaO₃ P2₁/c Na₃AlF₆ NaSr₃TaO₆ 4.11 −0.056Na₅TaO₅—Sr₂Ta₂O₇—SrO R3c K₄CdCl₆ NaSrBO₃ 4.10 −0.020 Na₃BO₃—Sr₃B₂O₆P2₁/c None BaNaBO₃ 4.00 −0.171 NaBO₂—BaO C2/m Na₂CO₃ Ba₃NaTaO₆ 3.63−0.061 Na₅TaO₅—Ba₄Ta₂O₉—BaO R3c K₄CdCl₆ Na₅WNO₄ 3.31 −0.012Na₂O—Na₄WN₂O₂—Na₄WO₅ Cmc2₁ None Ba₃NaNbO₆ 3.26 −0.067Na₅NbO₅—BaO—Ba₃Nb₂O₈ R3c K₄CdCl₆ Na₄MoN₂O₂ 2.58 −0.040 Na₃MoN₃—Na₅MoNO₄P1 Na₄WO₂N₂ Na₄WN₂O₂ 2.21 −0.025 Na₃WN₃—Na₅WNO₄ P1 Na₄WO₂N₂ NitrideCompounds Na₅WNO₄ 3.31 −0.012 Na₂O—Na₄WN₂O₂—Na₄WO₅ Cmc2₁ None NaLi₃H₈N₄2.97 −0.007 NaH₂N—LiH₂N 14 LiNH₂ Na₄MoN₂O₂ 2.58 −0.040 Na₃MoN₃—Na₅MoNO₄P3 Na₄WO₂N₂ NaSr₄B₃N₆ 2.22 −0.256 BN—Sr₂N—Na₃BN₂—SrN Im3m Sr₉B₆N₁₂Na₄WN₂O₂ 2.21 −0.025 Na₃WN₃—Na₅WNO₄ P1 Na₄WO₂N₂ Ba₄NaB₃N₆ 2.18 −0.027Ba₃B₂N₄—Na₃BN₂ Im3m Sr₉B₆N₁₂

For Na metal anodes, Tables 11-17 list the binary and ternary compoundsthat passed the screens containing F, O, Cl, N, Br, S, and C anionsrespectively. Table 18 lists all quaternary compounds for lithium metalanodes, which contained only O and N anions. Na solid electrolytes forroom temperature batteries have been studied less than Li solidelectrolytes due to the relatively modest performance of Na solidelectrolytes and electrodes. The most famous Na solid electrolyte isNa-beta alumina (Na-β″-Al₂O₃), which has a composition given by(Na₂O)_(1+x)(Al₂O₃)₁₁, where x ranges from 0 to 0.57. Na-beta alumina isnot in the OQMD dataset. The compound that is nearest in composition toNa-beta alumina in the OQMD is Al₂O₃, which did not pass the screens.However, four ternary Na—Al—O compounds were identified that passed thescreens, including NaAlO₂, Na₇Al₃O₈, Na₅AlO₄, and Na₁₇Al₁₅O₁₆. Thisfinding of Na—Al—O coatings for Na anodes differed from the finding forLi anodes, where no ternary Li—Al—O compounds passed the screens.

The set of oxide coatings for Na metal anodes included 63 compoundscomprising 24 binaries, 26 ternaries, and 13 quaternaries, making it thelargest set among the anode/anion pairs that were considered. Fourteencompounds were identified with the formula R₂O₃, where R is a rare earthincluding Y, Lu, Dy, Tm, Ho, Sc, Er, Tb, Gd, Nd, Sm, Pr, Ce, and La.Seven ternary oxides were also identified with the formula NaRO₂, whereR is a rare earth including Y, Er, Tb, Gd, Nd, Sc, and Pr. Six ternarysulfides were identified for Na anodes, including five compounds withthe formula NaRS₂, where R is a rare earth including Lu, Er, Ho, Y, andTm. Whereas, for Li anodes, no ternary sulfides were identified.

Tables 19-25 list binary and ternary coatings for Mg anodes containingF, O, Cl, N, Br, S, and C anions, respectively. No quaternary coatingswere identified for Mg anodes. Electronic bandgaps and stabilities arereported in eV. Stabilities are calculated with respect to thenearest-energy set of competing phases. Space group and prototypestructure are also listed.

TABLE 19 Fluoride binary and ternary coatings for Mg metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLiF 9.56 −1.050 LiF₂—Li₃F₂ Fm3m B1 SmF₃ 8.38 −1.680 SmF₂—F₂ Pnma YF₃HoF₃ 8.32 −1.713 HoF₂—F₂ Pnma YF₃ ErF₃ 8.31 −2.450 Er₂F₃—F₂ Pnma YF₃EuF₂ 7.94 −0.925 Eu₂F₃—EuF₃ Fm3m CaF₂ MgF₂ 7.64 −1.487 MgF₃—MgF P4₂/TiO₂ mnm SrF₂ 7.43 −1.232 SrF₃—SrF Fm3m CaF₂ CaF₂ 7.41 −0.965 Ca₂F₃—CaF₃R3m None YbF₂ 7.31 −1.287 YbF₃—YbF P4₂/ C4 mnm BaF₂ 7.05 −0.846BaF₃—Ba₂F₃ Fm3m None NaF 6.65 −0.908 Na₃F₂—NaF₂ Fm3m B1 TernaryMagnesium-Containing Compounds KMgF₃ 7.85 −0.038 K₂MgF₄—MgF₂ Pm3m CaTiO₃NaMgF₃ 7.51 −0.025 NaF—MgF₂ Pnma GdFeO₃ RbMgF₃ 7.47 −0.020 Rb₂MgF₄—MgF₂P6₃/ BaFeO₂ + x mmc Cs₄Mg₃F₁₀ 7.00 −0.041 CsF—MgF₂ Cmca Sr₄Mn₃O₁₀ Mg₃NF₃4.23 −0.011 Mg₂NF—MgF₂ Pm3m U₄S₃

TABLE 20 Oxide binary and ternary coatings for Mg metal anodes.Competing Space Band Gap Stability Phases Group Prototype BinaryCompounds BeO 7.90 −1.584 Be—Be₂O₃ P6₃mc B4 MgO 4.97 −1.010 Mg₂O—Mg₄O₅Fm3m B1 Y₂O₃ 4.37 −0.823 Y₄O₅—YO₂ Ia3 Mn₂O₃ Lu₂O₃ 4.22 −1.056 Lu₄O₅—O₂Ia3 Mn₂O₃ Dy₂O₃ 4.17 −0.989 Dy₄O₅—O₂ Ia3 Mn₂O₃ Tm₂O₃ 4.16 −0.859TmO₂—Tm₄O₅ I2₁₃ Sm₂O₃ Ho₂O₃ 4.14 −1.011 Ho₄O₅—O₂ Ia3 Mn₂O₃ Sc₂O₃ 4.12−0.840 ScO₂—Sc₄O₅ Ia3 Mn₂O₃ Er₂O₃ 4.12 −1.016 Er₄O₅—O₂ Ia3 Mn₂O₃ Tb₂O₃4.09 −0.488 TbO—Tb₇O₁₂ Ia3 Mn₂O₃ Gd₂O₃ 4.08 −0.969 Gd₄O₅—O₂ Ia3 Mn₂O₃CaO 3.75 −1.134 Ca₂O₃—Ca₂O Fm3m B1 YbO 3.52 −0.950 Yb₄O₅—Yb₃O₂ Fm3m B1EuO 2.81 −0.797 Eu₂O—Eu₃O₄ Fm3m B1

TABLE 21 Chloride binary and ternary coatings for Mg metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLiCl 6.25 −0.772 LiCl₂—Li₃Cl₂ F4 ₃m B₃ BaCl₂ 5.69 −0.648 BaCl₃—Ba₂Cl₃Fm3m CaF₂ YbCl₂ 5.63 −0.250 Yb₆Cl₁₃—Yb P4₂/mnm C4 MgCl₂ 5.62 −0.883MgCl—MgCl₃ R3m CdCl₂ SrCl₂ 5.53 −0.962 SrCl—SrCl₃ Fm3m CaF₂ CaCl₂ 5.48−0.723 Ca₂Cl₃—CaCl₃ P4₂/mnm TiO₂ KCl 5.30 −0.732 KCl₂—K₃Cl₂ Fm3m B1EuCl₂ 5.19 −0.837 EuCl—EuCl₃ Pnma PbCl₂ NaCl 5.18 −0.727 NaCl₂—Na₃Cl₂Fm3m B1 CsCl 5.08 −0.629 Cs₃Cl₂—CsCl₂ Fm3m B1 RbCl 4.98 −0.715Rb₃Cl₂—Cl₂ R3m L1₁ TmCl₃ 4.92 −0.857 TmCl₂—Cl₂ R3c FeF₃ YCl₃ 4.77 −0.834YCl₂—Cl₂ C2/m RhBr₃ TbCl₃ 4.74 −0.822 TbCl₂—Cl₂ P4₂/mnm None CeCl₃ 4.71−1.252 Ce₂Cl₃—Cl₂ P2₁/m UCl₃ PrCl₃ 4.46 −0.813 PrCl₂—Cl₂ P2₁/m UCl₃NdCl₃ 4.43 −0.807 NdCl₂—Cl₂ P2₁/m UCl₃ GdCl₃ 4.37 −0.799 GdCl₂—Cl₂ P6₃/mUCl₃ DyCl₃ 3.75 −0.818 DyCl₂—Cl₂ Cmcm NdBr₃ LaCl₃ 3.74 −0.855 LaCl₂—Cl₂P6₃/m UCl₃ LuCl₃ 3.19 −0.791 LuCl₂—Cl₂ P6₃/mmc DO₁₉ TernaryMagnesium-Containing Compounds CsMgCl₃ 5.34 −0.031 Cs₂MgCl₄—MgCl₂ CmcmBaNiO₃ Cs₂MgCl₄ 5.16 0.000 CsMgCl₃—CsCl Pnma Cs₂CuCl₄ RbMgCl₃ 5.04−0.028 RbCl—MgCl₂ P6₃/mmc None K₂MgCl₄ 4.99 −0.003 KCl—MgCl₂ I4/mmmK₂MgF₄

TABLE 22 Nitride binary and ternary coatings for Mg metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary Compounds BN4.38 −1.071 B₁₃N₂—N₂ P6₃/mmc BN AlN 4.34 −1.275 Al₃N—N₂ P6₃mc B4 Be₃N₂3.52 −0.710 Be₂N—N₂ Ia3 Mn₂O₃ Mg₃N₂ 1.78 −0.351 Mg₂N—N₂ Ia3 Mn₂O₃Ternary Magnesium-Containing Compounds MgSiN₂ 4.29 −0.224 Mg₃N₂—Si₃N₄Pna2₁ NaFeO₂ Mg₃NF₃ 4.23 −0.011 Mg₂NF—MgF₂ Pm3m U₄S₃ MgBe₂N₂ 4.16 −0.083Mg₃N₂—Be₃N₂ P3m1 La₂O₃ MgB₉N 1.82 −0.064 B—MgB₇—BN R3m None

TABLE 23 Bromide binary and ternary coatings for Mg metal anodes. BandCompeting Space Gap Stability Phases Group Prototype Binary CompoundsLiBr 5.15 −0.673 LiBr₂—Li₃Br₂ F4 ₃m B3 YbBr₂ 4.80 −0.783 YbBr₃—YbBr PnnmNone SrBr₂ 4.72 −0.827 SrBr₃—SrBr Pnma PbCl₂ CaBr₂ 4.68 −0.898CaBr₃—CaBr Pnnm CaCl₂ MgBr₂ 4.63 −0.770 MgBr—MgBr₃ P3m1 CdI₂/ Mg(OH)₂BaBr₂ 4.48 −0.557 Ba₂Br₃—BaBr₃ Pnma PbCl₂ KBr 4.45 −0.622 K₃Br₂—KBr₂Fm3m NaCl RbBr 4.42 −0.613 Rb₃Br₂—RbBr₂ Fm3m B1 CsBr 4.41 −0.543CsBr₃—Cs₃Br₂ Fm3m B1 EuBr₂ 4.40 −0.812 EuBr₃—EuBr P4/n SrBr₂ NaBr 4.36−0.639 NaBr₃—Na₃Br₂ Fm3m B1 GdBr₃ 3.80 −0.731 GdBr₂—Br₂ C2/m RhBr₃ PrBr₃3.57 −0.292 Pr₂Br₅—Br₂ P6₃/m UCl₃ CeBr₃ 3.55 −0.299 Ce₂Br₅—Br₂ P2₁/mUCl₃ LaBr₃ 3.10 −0.312 La₂Br₅—Br₂ P6₃/m UCl₃ SmBr₃ 2.87 −0.687 SmBr₂—Br₂Cmcm NdBr₃ NdBr₃ 2.85 −0.679 NdBr₂—Br₂ Cmcm NdBr₃ ErBr₃ 2.27 −0.653ErBr₂—Br₂ P6₃/mmc DO₁₉ Ternary Magnesium-Containing Compounds CsMgBr₃4.23 −0.041 MgBr₂—CsBr Cmcm BaNiO₃

TABLE 24 Sulfur binary and ternary coatings for Mg metal anodes.Competing Space Band Gap Stability Phases Group Prototype BinaryCompounds Li₂S 3.66 −0.561 Li₃S—LiS Fm3m None MgS 2.85 −0.608 MgS₂—Mg₂SR3m L1₁ Na₂S 2.63 −0.377 Na₃S—NaS Fm3m CaF₂ SrS 2.57 −0.666 SrS₂—Sr₃S₂Fm3m B1 CaS 2.50 −0.988 Ca₂S₃—Ca₂S Fm3m B1 K₂S 2.44 −0.339 K₃S—KS Fm3mCaF₂ YbS 2.33 −0.431 Yb₃S₂—Yb₇S₈ Fm3m None BaS 2.24 −0.594 Ba₂S—Ba₂S₃Fm3m B1 Cs₂S 2.21 −0.240 Cs₃S—CsS Pnma None Rb₂S 2.21 −0.297 RbS—Rb₃SFm3m CaF₂ EuS 2.07 −0.701 Eu₃S₄—Eu₂S Fm3m NaCl TernaryMagnesium-Containing Compounds Lu₂MgS₄ 2.13 −0.011 MgS—Lu₂S₃ Fd3mAl₂MgO₄

TABLE 25 Carbide binary and ternary coatings for Mg metal anodes. BandSpace Gap Stability Competing Phases Group Prototype Binary CompoundsAl₄C₃ 1.47 −0.098 C—Al R3m None Be₂C 1.41 −0.234 Be—C Fm3m CaF₂ TernaryMagnesium-Containing Compounds MgAl₂C₂ 1.90 −0.002 Mg—Al₄C₃—C P3m1 La₂O₃MgB₂C₂ 1.16 −0.070 Mg—C—MgB₁₂C₂ Cmca None

For Mg metal anodes, Tables 19-25 list the binary and ternary compoundsthat passed the screens containing F, O, Cl, N, Br, S, and C anionsrespectively. No quaternary compounds passed the screens for Mg anodes.Five ternary fluoride coatings were identified for Mg anodes, whereas noternary fluorides passed the screens for Li or Na anodes. Nine coatingswere identified with the formula R₂O₃, where R is a rare earth includingY, Lu, Dy, Tm, Ho, Sc, Er, Tb, and Gd. Ten coatings were identified withthe formula RCl₃, where R is a rare earth including Tm, Y, Tb, Ce, Pr,Nd, Gd, Dy, La, and Lu. One ternary sulfide was identified, Lu₂MgS₄.

Each compound that passed the screens shared a tie line with the anodemetal within the computed convex hull.

These coatings may be employed at nanometer thickness, where ionicconductivity of the coatings does not strongly impact cell impedance.The ionic conductivity for at least some embodiments of the compoundsmay enable these compounds to be used not just as anode coatings, butalso as thick solid electrolytes that enable transport between the anodeand cathode.

CONCLUSIONS

It was found that many solid electrolyte and electrode coating materialsin the literature react with Li anodes to form unanticipated phases,including phases that are electronically conductive and thereforeprevent passivation of the anode/electrolyte interface. The OQMD wasscreened to identify coatings for Li, Na, and Mg metal anodes thatexhibit chemical equilibrium with the anode metals and that areelectronic insulators. Ninety-two promising coatings were identified forLi anodes, as well as 118 for Na anodes, and 97 for Mg anodes. Thesecoatings included binary, ternary, and quaternary compounds. For Lianodes, Li-containing ternary coatings were identified, including sevenoxides and 21 nitrides, but no fluorides or sulfides. For Na anodes,Na-containing ternaries were identified, including 26 oxides, ninenitrides, and six sulfides, but no fluorides. For Mg anodes,Mg-containing ternaries were identified, including five fluorides, fournitrides, and one sulfide, but no oxides. A variety of chloride,bromide, and carbide coatings were also identified.

Many of the new coatings share similar compositions and can therefore begrouped into classes. Several new classes of coatings were identifiedfor Li anodes, including Li_(x)MN₄ (x=5, 6, 7; M=transition metal), R₂O₃(R=rare earth), and LiRO₂. For Na anodes, classes of coatings wereidentified, including R₂O₃, NaRO₂, and NaRS₂. For Mg anodes, classes ofcoatings were identified, including R₂O₃ and RCl₃. Within the ninety twocompounds identified for Li anodes, only Li₃N and Li₇La₃Hf₂O₁₂ have beenstudied extensively as solid electrolyte materials.

Example 2: Coatings for Lithium Anodes and Solid-State Electrolytes inLithium Batteries

In this example, the Open Quantum Materials Database was used to searchfor coating materials that exhibit stable equilibrium with both Li metaland various solid electrolyte materials, that are electronic insulators,and that contain Li sublattices. The requirement for a Li sublattice wasrelaxed for the binary compounds. The pentenary compounds that passedthe screens contained only small concentrations of Li, so thesecompounds were excluded from the search. The coatings identified includebinaries, and Li-containing ternaries and quaternaries. Thecomputational methodology was the same as that described in detail inExample 1.

Coatings that are particularly chemically stable with respect to bothlithium metal anodes and various solid electrolyte materials wereidentified. A general trend can be observed, whereby the oxide andnitride coatings tend to exhibit stable equilibrium with Li₇La₃Zr₂O₁₂,LiLaTi₂O₆, Li₃PO₄, and Li₇PN₄ solid electrolytes, while the fluoride,chloride, bromide, and sulfide coatings are more likely than oxides ornitrides to exhibit stable equilibrium with LiTi₂P₃O₁₂, Li₃PS₄,Li₁₀GeP₂S₁₂, and Li₆PS₅Br solid electrolytes. For example, CaF₂ and YbF₂are coating materials that are particularly well-suited for coating onlithium metal anodes and also stable on Li₃PS₄ electrolyte materials.And, as another illustration, Li₆WN₄ and Li₂CN₂ are coating materialsthat are particularly well-suited for coating on lithium metal and alsoon Li₇La₃Zr₂O₁₂ electrolyte materials. The full set of coatings that areparticularly stable on lithium metal anodes and also on variouselectrolyte materials is presented in Tables 26-32.

Tables 26-32. Coatings that exhibit stable equilibrium with both Limetal and various solid electrolyte materials, including Li₇La₃Zr₂O₁₂,LiLaTi₂O₆, Li₃PO₄, LiTi₂P₃O₁₂, Li₃PS₄, Li₁₀GeP₂S₁₂, Li₆PS₅Br, and Li₇PN₄electrolytes. All coatings that are listed exhibit stable equilibriumwith Li metal. The existence of stable equilibrium between a coating andan electrolyte material is indicated with an ‘X’.

TABLE 26 Fluoride Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries LiF X X X X X X X X EuF₂ X XX X X X X X SrF₂ X X X X X CaF₂ X X X X YbF₂ X X X X X X X

TABLE 27 Oxide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂ Li₃PS₄Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries BeO X X X X X X X X Li₂O X X X XY₂O₃ X X X Lu₂O₃ X X X Dy₂O₃ X X Tm₂O₃ X X X Ho₂O₃ X X X Er₂O₃ X X Gd₂O₃X X X Nd₂O₃ X X X X Sm₂O₃ X X X X Pr₂O₃ X X X X La₂O₃ X X X X CaO X X XX YbO X X X X X EuO X X X X Ternaries LiGdO₂ X X X X Li₂HfO₃ X X XLiDyO₂ X X X X LiTbO₂ X X X X LiHoO₂ X X X LiErO₂ X X X X LiScO₂ X X XQuaternaries Li₇La₃Hf₂O₁₂ X X X X Li₁₆Nb₂N₈O X X X Li₁₆Ta₂N₈O X XLiSmEu₂O₄ X X X X

TABLE 28 Chloride Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries LiCl X X X X X X X X BaCl₂ XX X X X YbCl₂ X X X X X SrCl₂ X X X X KCl X X X X X X EuCl₂ X X X X NaClX X X X X X CsCl X X X X X X X RbCl X X X X X X X Ternaries Li₄NCl X

TABLE 29 Nitride Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries AlN X X Be₃N₂ X X LaN X Li₃NX Ternaries Li₂CN₂ X X X X Li₂SiN₂ X X Li₃BN₂ X X Li₇TaN₄ X Li₇NbN₄ X XLi₆WN₄ X X X X Li₇VN₄ X X X LiBeN X X Li₅ReN₄ X X X X Li₆MoN₄ X X X XLi₈TeN₂ X LiMgN X Li₅Br₂N X Li₃ScN₂ X Li₄NCl X Li₄HN X Li₈SeN₂ X Li₂ZrN₂X X X LiCaN X Li₁₀BrN₃ X SrLi₄N₂ X Quaternaries Li₁₆Nb₂N₈O X X XLi₁₆Ta₂N₈O X X Li₅La₅Si₄N₁₂ X Li₄Ca₃Si₂N₆ X Sr₄LiB₃N₆ X X Li₅Ce₅Si₄N₁₂ XX LiEu₄B₃N₆ X LiCa₄B₃N₆ X Sr₃Li₄Si₂N₆ X SrLi₂CrN₃ X X X X

TABLE 30 Bromide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries LiBr X X X X X X X X YbBr₂ XX X X X SrBr₂ X X X X X BaBr₂ X X X X X KBr X X X X X X X X RbBr X X X XX X X X CsBr X X X X X X X X EuBr₂ X X X X NaBr X X X X X X X TernariesLi₅Br₂N X Li₁₀BrN₃ X

TABLE 31 Sulfide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries Li₂S X X X X X X SrS X X X XX X X CaS X X X X X X YbS X X X X X X X BaS X X X X EuS X X X X

TABLE 32 Carbide Coatings Li₇La₃Zr₂O₁₂ LiLaTi₂O₆ Li₃PO₄ LiTi₂P₃O₁₂Li₃PS₄ Li₁₀GeP₂S₁₂ Li₆PS₅Br Li₇PN₄ Binaries Be₂C Ternaries Li₂CN₂ X X XX LiBC X

The word “illustrative” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein as“illustrative” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Further, for the purposes ofthis disclosure and unless otherwise specified, “a” or “an” means “oneor more”.

The foregoing description of illustrative embodiments of the inventionhas been presented for purposes of illustration and of description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed, and modifications and variations are possible inlight of the above teachings or may be acquired from practice of theinvention. The embodiments were chosen and described in order to explainthe principles of the invention and as practical applications of theinvention to enable one skilled in the art to utilize the invention invarious embodiments and with various modifications as suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A coated anode comprising: an anode comprisinglithium metal or an alloy of lithium with one or more additional metalelements; and a coating on at least a portion of the anode, wherein thecoating comprises a metal sulfide selected from SrS, CaS, YbS, andcombinations thereof.
 2. A lithium battery comprising: a coated anodecomprising: an anode comprising lithium metal or an alloy of lithiumwith one or more additional metal elements; and a coating on at least aportion of the anode, wherein the coating comprises a metal sulfideselected from SrS, CaS, YbS, and combinations thereof; a cathode inelectrical communication with the metal anode; and an electrolytedisposed between the coated anode and the cathode.
 3. The battery ofclaim 2, wherein the electrolyte is a sulfide solid electrolyte.
 4. Thecoated anode of claim 1, wherein the coating comprises SrS.
 5. Thecoated anode of claim 1, wherein the coating comprises CaS.
 6. Thecoated anode of claim 1, wherein the coating comprises YbS.
 7. Thecoated anode of claim 1, wherein the coating is a single phase of themetal sulfide.
 8. The coated anode of claim 1, wherein the coatingcomprises a mixture of metal sulfide phases.
 9. The coated anode ofclaim 1, wherein the coating has a thickness in the range from 0.1 nm to1000 nm.
 10. The coated anode of claim 1, wherein the anode is a lithiummetal anode.
 11. The battery of claim 2, wherein the coating comprisesSrS.
 12. The battery of claim 2, wherein the coating comprises CaS. 13.The battery of claim 2, wherein the coating comprises YbS.
 14. Thebattery of claim 2, wherein the coating is a single phase of the metalsulfide.
 15. The battery of claim 2, wherein the coating comprises amixture of metal sulfide phases.
 16. The battery of claim 2, wherein thecoating has a thickness in the range from 0.1 nm to 1000 nm.
 17. Thebattery of claim 2, wherein the anode is a lithium metal anode.